Learning Objectives


• Describe the infrastructure and anatomy of the heart.

• Relate Poiseuille’s law to hemodynamics.

• Explain the basic embryology of heart formation.

• Recall the pump cycle of the heart.

• Discuss the size, shape, and position of the heart.

• Summarize imaging methods for determining the normalcy or disease state of the heart.


Simple concepts govern the interactions between the heart and body. The unique structure and function defines disease processes, diagnosis and treatment for each organ. The format used in this tutorial uses a specific format, conforming to the principles outlined for each organ.

Each structure though a unique biological unit, is part of a system that is bigger and more powerful than itself. The heart has to be connected to the other organs and systems in order to survive.

As Biological Unit
The heart is a hollow organ with a muscular wall consisting of an inner endothelial lining, a thick muscular layer, and a double outer layer called the pericardium.

Links and Connections
The heart has an intimate connection to all the tissues and cells of the body from the tip of the toes to the crown of the head. The systemic arterial connection originates from the aorta with connections via the brachiocephalic, mesenteric, renal and peripheral arterial systems. The systemic veins join to form the inferior vena cava that drains the lower part of the body and superior vena cava that drains the upper part. The lymphatic system flows from the heart into the thoracic and right lymphatic ducts. The nerve supply is via connections to the sympathetic (celiac axis) and parasympathetic (vagus) systems. Hormonal connections include interaction with epinephrine, nor epinephrine, and thyroid hormones, but the atrial muscles also produce hormones.   The atrial natriuretic peptide (ANP)  is one hormone which helps maintain homeostasis of water, sodium, potassium and adipose tissue.

Units to Unity
The concept of units to unity reflects the importance of each unit within the system being an important part of something larger. The cardiovascular system contains the heart, which in turn is part of every system in the body. This vital organ contains pumps and a tubular system of vessels and capillaries.

Dependence and Independence
The heart cannot function alone and requires centrally based innervations and signaling of the neurohormonal axis to instruct it as to the needs of each of the other systems of the body.

Time Growth and Aging
The heart arises from the primitive mesenchyme as a single tube in the embryo. The single tube becomes a two chambered system by septation, growth and resorption, and selective apoptosis. The heart ages well, though atherosclerosis of the coronary arteries is part of the aging process and is a common cause of morbidity and mortality in the elderly.

The heart lies within the thoracic cavity of the chest, in close association with the lungs. It lies in an eccentric position, slightly toward the left of middle, and divides the chest into right and left sides.

The forces that govern cardiac function are mostly mechanical in origin. The forces created by contraction and relaxation enable blood to flow. The heart fills with passive and active mechanisms by ongoing forward forces (pushing force from behind) and forces that also pull the blood (pulling forces from in front).  Valves between the atria, ventricles, and the great vessels, prevent backflow, allowing forward flow into the pulmonary and systemic circulations.

Simple concepts govern the interactions between the heart and body.The heart acts as the transport system of required vital nutrients allowing function of all parts of the body.  In particular it transports oxygen and carbon dioxide. Transportation of metabolic substrates to the capillaries and diffusion across pressure gradients into the intercellular spaces, and transportation through the cell membrane occur through circulation of nutrient rich arterial flow. Waste products transport in the opposite direction, from the cell to the interstitium, into the capillaries, and finally into the venous system for transport to the excretory organs.

The heart responds with beat to beat accuracy to the bodies needs, balances right and left circulations, as well as the differential needs within the vast range of physiologic conditions from sleep to intense exercise.

States of Being – Health and Disease
By virtue of its function as a pump, diseases related to the heart are of a mechanical nature. The most common malady of the heart is ischemic disease. Myocardial failure results in venous congestion due to output reduction by the chambers to the arterial circulation. Often the mechanical causes of disease such as stenosis of the coronary arteries, acute coronary thrombosis, or valvular stenosis, require minimally invasive or surgical procedures to open blockages. When the myocardial forces have been reduced to levels where function is impaired, the range of therapies relate to enhancing myocardial contractility, or reducing the workload.  There is a point where conventional therapy fails and the only hope for survival is heart transplantation.

Principles of Circulation

In a tube, the volume of the flow rate changes due to the pressure differences, length and diameter of the tube and the viscosity of the fluid.

The heart is a muscular organ specifically designed for the transport of blood by acting as a pump. At the terminal end of the arterial circulation is a capillary system structurally designed in network formation to increase the surface area available for rapid and efficient metabolic exchange.

Multiple tubular systems exist throughout the body. Classical examples include the airway, venous, lymphatic, ductal, gastrointestinal, and genitourinary systems. Flow occurs when a pressure difference exists between the two sides of the tubes.

The velocity of flow relates to diameter, resistance, friction, and pressure. Velocity of flow also depends on whether the flow is laminar or turbulent. Poiseuille’s law states that the flow rate depends on the pressure differences between one end of the tube and the other. Thus, if the driving pressure doubles, the flow rate also doubles, as long as the radius remains constant. The radius of the tube, however, is very important. Poiseuille found that if either the length or viscosity doubled there was a reduction of the flow rate by half. He found that changes in the radius also affected the flow rate, but not as little as expected. Due to the inverse relationship of the flow volume to flow viscosity and the direct relationship to tube radius, doubling the radius increases the flow rate by sixteen times!

Though a significant finding, Poiseuille dealt with uniform tubes with the same radius throughout the length. Due to the elasticity of arterial walls, which expand and contract with the heart, flow in the body does not adhere to this law exactly. Remember, viscosity changes in the body due to disease processes or hydration.

Key Points of Poiseuille’s Law

1. An increase in pressure difference across the vessel results in an increase in flow rate.
2. Increasing diameter also increases flow rate.
3. Flow rate decreases with an increase in length.
4. Viscosity increases result in flow rate decrease.

            Reynold’s number = inertia (drag) forces/viscous force

Inertia forces are directly proportional to the density of fluid, velocity of fluid and length of tube

Laminar flow occurs with low drag forces and high viscous forces and is characterized by smooth constant fluid motion. Turbulent flow on the other hand occurs with high Reynolds numbers, is characterized by chaotic patterns of flow and occurs when inertial (drag) forces dominate. These changes occur in the normal individual under certain states, such as during exercise, or with disease for example with stenosis of vessels.

Causes of Reynolds Number Increases

1. Increases in flow speed.
2. Diameter increases.
3. Density increases.
4. Viscosity decreases.


Laminar flow through the heart is demonstrated through the use of color Doppler sonography. Note the homogeneous color (blue) of forward flow in the ventricle and homogeneous yellow orange color of the atrium.  Image courtesy of Philips Healthcare, Bothell, WA.


This diagram demonstrates the creation of turbulent flow through alteration of the straight flow pattern to a disorganized flow pattern due to a vessel stenosis. Image courtesy of Philips Healthcare, Bothell, WA.


Factors Affecting Velocity Flow Profiles

Mechanical properties of blood
Flow velocity



This image of the internal carotid artery (ICA) stenosis demonstrates turbulent flow (yellow arrow).  The color shows the chaotic pattern of flow in the post stenotic segment thorough the intermixing of the blue and orange color tags.
Image courtesy of Philips Healthcare, Bothell, WA.         
Mitral Regurgitation
This color flow Doppler echo of the heart shows a 4 chamber view, and demonstrates a chaotic heterogeneous color pattern in the atrium consisting of orange, reds, yellows, and blues and indicates mitral regurgitation. The mitral incompetence is demonstrated by regurgitant blue jet from the left ventricle into the left atrium.
Courtesy Philips Healthcare

The cardiovascular system is beautifully designed to enable rapid and efficient delivery of blood to the organs. Not only is the delivery rapid, but the design is such that differential needs are accommodated. Thus, during exercise the skeletal muscle is hyperactive while the gastrointestinal tract is not active. Thus, blood is shunted to the skeletal muscle and away from the gastrointestinal tract.

What a system! If we could only have such a system in the world that delivers adequate amount of supplies efficiently to the regions that most need the substrates at a particular moment in time.


Quiz Me

The volume of flow has a direct relationship to the length of a tube.

True  False

Principles of Circulation: The Heart as Pump

All functional devices work on the principal that they receive, process and export.

A pump is a mechanical device that moves gases or fluids. In order for a pump to be effective it must pump out what it receives.

The heart is a functional structure and therefore it conforms to the principles of all other functional structures. In keeping with these principles it therefore receives a product, processes it and then exports the product. In the case of the heart, it receives blood, accumulates an adequate volume while it relaxes and then gathers forces to export it by contraction.
Courtesy of: Ashley Davidoff, M.D.

In order for the heart to be effective in the body it needs to pump out what the body needs and be able to receive what is returned to it.

The heart is a positive displacement pump, meaning that it causes the blood to move by first trapping a fixed amount of blood in the chambers, and then forcing the blood into the outflow system by contraction. It accomplishes this by a reciprocal motion of relaxation and contraction. The pumping chamber reduces its volume by muscular contraction, while the receiving chamber increases its volume by relaxation. The contraction forces the blood to move forward, and the relaxation creates a relative vacuum allowing blood to be sucked into the heart.

The heart consists of two such pumps that are connected in series, allowing for a pulmonary circulation and a left-sided systemic circulation.

This diagram shows the right ventricle and lobar pulmonary arteries in blue and the left ventricle and aorta in red. The right sided component of the pump (blue) receives blood from the systemic circulation via the SVC and IVC and pumps it to the lungs.  The left sided circulation (red) receives oxygenated blood and pumps it to the systemic circulation.
Note that the lobar pulmonary arteries have the same, irregular, dichotomous, branching pattern as the lobar bronchi and give 3 major branches to the right lung (right upper, right middle and right lower lobe arteries) and two to the left (left upper and left lower pulmonary arteries).
Courtesy of: Ashley Davidoff, M.D. 32687b01

The heart is made of a special type of muscle which has the innate properties of contractile function.


The contractile properties of the myocardium enable the heart pump. In this diagram a single contraction is demonstrated, forcing the blood through the aortic valve, (not shown) into the aorta, against the resistance or afterload of the systemic circulation which allows the generation of the pressure. The force generated causes blood to flow from a high pressure proximally to a low pressure in the capillaries.
Courtesy of: Ashley Davidoff, M.D.

The blood flows from a high to low pressure system via arterioles, capillaries, venules and then into the venous system, which returns the blood to the heart.

The full systemic circulation is shown in this diagram with the arterial side (red), capillary (red and blue cluster), and venous components. Courtesy of: Ashley Davidoff, M.D.
Note the difference in the pressures between the left side of the circulation and the right. The left ventricular pressure reaches a systolic of 120 mmHg, while the right atrial pressure is close to zero. This large difference allows blood to flow through the circulation pressure principles. Courtesy of: Ashley Davidoff, M.D.

In an average lifetime, the heart beats more than two and a half billion times. Think about this number a few times – imagine what an unbelievable engineering feat nature has accomplished. In fact it is not just a pump that moves in and out. There is second to second, and beat to beat variation so that it continuously changes its patterns of contraction and relaxation, always accommodating bodily needs.  The heart circulates the body’s blood supply about 1,000 times each day, circulating 5-6000 liters of blood through 62,000 miles (length of two and half times around the earth).  An average adult body contains about five liters of blood.

The beat to beat to beat variation allows the output from the left to be reconciled with what is coming back in the return, so that congestion does not occur.  In addition, physiology is a dynamic process and the demands of each system in the body changes based on special needs and activities.  The heart also has to accommodate to these changing needs distributing a fixed amount of blood to the regions that need it most at any one time. During exercise for example, the skeletal muscle requires increased flow due to the increased metabolic demand, while the gastrointestinal system uses less flow due to a resting state. Blood shunts from the one system to the other.  The controlling mechanisms at both the local and systemic levels are simply elegant and complex, but effective.

Structure of the Heart

Structural principles are grounded in the notion that biological units have characteristic and defining size, shape, position and character, with connections via neurovascular bundles, ducts and lymphatics to the system at large.

The size of heart is characteristically described as being fist-sized and can be measured in many ways including centimeters (cm), cubic centimeters (cc), or grams (g).  The most useful, functionally, is the chamber volume at end diastole and end systole. The end diastolic volume of each ventricle is about 150 ccs and end systolic volume is about 70 ccs.  Conceptually the four chambers of the heart have been described as two upper receiving chambers and two lower pumping chambers but the structural characteristics of each is unique.  In general though, the atria, as receiving chambers, tend to be round and the ventricles oval, or conical.

Traditionally, the position of the heart is considered to be on the left side and true to tradition, it is mostly left-sided with the apex of the heart pointed to the left.  The right atrium and ventricle are dominantly positioned to the right of midline. The left ventricle has a central position while the ventricle has a left-sided location.
The heart is demarcated by:

      • A point nine centimeters to the left of the midsternal line (apex of the heart);
      • the seventh right, sternocostal articulation; the upper border of the third right, costal cartilage one centimeter from the right sternal line;
      • The lower border of the second left, costal cartilage; two and a half centimeters from the left lateral, sternal line.

The heart is made of striated, syncytial muscle with a surrounding membrane (pericardium) consisting of a membranous, inner, serous layer and an outer, sero-fibrous compose layer.

The connections of the heart to the rest of the cardiovascular system are via the arteries, veins, nerves and endocrine system. Coronary arteries provide the heart blood supply, venous drainage via the cardiac veins, and lymphatics via the pericardial system.  Parasympathetic and sympathetic systems connect it to the autonomic nervous system, while the hormonal control is via natriuretic hormone, adrenaline, and nor adrenaline.

The main component parts of the heart include the right atrium, tricuspid valve, right ventricle, left atrium, mitral valve, and left ventricle.  The aortic valve and the pulmonary valve are part of the great vessels and vascular system that emanate from the heart.  They are included in part in the following discussion since they are the link to the systemic and pulmonary circulations, and their competence is necessary for normal function of the heart.

Structure of the Heart: The Basic Infrastructure of the Heart

From the outset, it is reasonable to conceptually visualize the infrastructure of the heart as a four-chambered box centered around a scaffolding that has a cross-like formation, with two smaller upper chambers and two larger lower chambers.

The scaffolding of the heart consists of a cross surrounded by four chambers. The upper smaller chambers are the receiving chambers and the lower larger chambers are the pumping chambers. Courtesy of: Ashley Davidoff, M.D.
The infrastructure of the heart is more complex and has 3 dimensions and 3 major septa. Between the two atria is the interatrial septum, and between the two ventricles is the interventricular septum. A third septum is in the z axis and is called the conal septum and lies between the aorta and the pulmonary artery, The conal septum has its base at the crux of the heart where all the septa meet together with many of the structures of the heart. The concept of the crux of the heart will evolve. Courtesy of: Ashley Davidoff, M.D.

The heart chambers do not lie in a vertical orientation.  The atria are relatively posteriorly and rightwardly placed and the ventricles are relatively anterior and leftward.  The right-sided structures tend to be anteriorly placed while the left are posteriorly placed.

The scaffolding of the heart can be represented by a cross, consisting of two upper smaller components, and two larger lower components. In this diagram, a heart with a young lady in the center is laying along the lines of the scaffolding. Her legs lie in the interventricular septum, her right arm is in the tricuspid valve annulus in the horizontal component of the cross, and her left arm is in the plane of the mitral annulus. Her head lies at the bottom of the interatrial septum. Only the most inferior aspect of the left and right atrium is depicted. Courtesy of: Ashley Davidoff, M.D.
The heart chambers do not lie in a vertical orientation but lie in an oblique plain. The atria are relatively posteriorly placed and the ventricles are relatively anterior. The atria also tend to be rightward placed while the ventricles tend to be leftward. The right sided structures tend to be anteriorly placed while the left are posteriorly placed. The septa have complex embryological origins and consist of many parts that have clinical relevance. In this diagram the crux of the heart is colored in pink and represents the parts contributed by the embryological tissue called the endocardial cushions. The interatrial septum consists of three embryological parts: sinus venosus (purple), the septum secundum (green), and the septum primum (pink). The interventricular septum consists of a muscular portion (red), and an endocardial cushion component (pink). The conal septum is part of the conus arteriosus and lies between the pulmonary artery and aorta and is colored in orange.
Courtesy of: Ashley Davidoff, M.D.
This diagram is slightly more complex but in general reveals the same concepts as described above, and shows the position of the right sided tricuspid valve and the mitral valve. In this diagram the crux of the heart and the endocardial portion of the interatrial septum and interventricular septum are colored in pink. The interatrial septum consists of the sinus venosus component (purple), the septum secundum (green) and the septum primum (pink) The interventricular septum consists of a muscular portion (red), and a endocardial cushion component (pink). The conal septum is part of the conus arteriosus, lies between the pulmonary artery and aorta and is colored in orange.
Courtesy of: Ashley Davidoff, M.D.

The vascular system and conduction system are organized around the scaffolding of the heart.

The aorta which is centered at the crux gives rise to two main arteries; the right and left coronary arteries whose tributaries course along the vertical and horizontal axis of the of the scaffolding .

The heart has a left and right arterial system. The vessels are formed around the cross of the heart, “vertically” along the interventricular septum and interatrial septum, and “horizontally” in the atrioventricular (A-V) grooves. The left coronary artery arises from the left coronary ostium and supplies one branch, the left anterior descending artery, that travels anteriorly on the anterior aspect of the interventricular septum, and one branch that travels in the atrioventricular groove (left circumflex). The right coronary artery has a branch that courses along the right atrioventricular groove and usually continues as the posterior descending artery on the posterior aspect of the interventricular groove, and commonly gives rise to the A-V nodal branch, at the back of the crux of the heart, which travels in the vertical axis in the interatrial septum.
Courtesy of: Ashley Davidoff, M.D.
The conduction system is also centered on the crux of the heart. The sinoatrial (S-A) node lies close to the SVC, and the system advances through the atrial wall to the atrioventricular node (A-V node) which lies anterior to the coronary sinus and IVC. The bundle of His extends along the A-V groove toward the superior aspect of the interventricular septum – at the crux of the heart, after which it divides into a right bundle branch that travels on the right side of the septum, and a left bundle branch that travels on the left side of the septum.
Courtesy of: Ashley Davidoff, M.D.
The basic infrastructure of the scaffolding of the heart is demonstrated by the pacing leads in this cross sectional CT with one lead (orange and purple) in the coronary sinus and therefore positioned in the atrioventricular groove (horizontal limb of the cross) and the second (pink/red) along the interatrial septum (pink) and interventricular septum (red) The crossroads is highlighted in green, and represents the true crux where the septal portions of the heart meet. All images courtesy of: Ashley Davidoff, M.D.


Quiz Me

What is the approximate volume change of the ventricles at end diastole and end systole?
(Note: You will be given 2 tries to answer this question, then the answer will be provided.)
70 ccs
150 ccs
80 ccs
220 ccs

Structure of the Heart: Histology

The layers of the heart conform to the basic pattern seen in the histology of other tubular structures except that the muscle layer dominates.

Tubular structures in the body have a basic structural makeup of an inner layer lined with an epithelial layer abutting the lumen, a middle functional layer and an outer protective layer or skin.  In the heart the inner layer is called the endocardium, the middle muscular layer is called the myocardium, and the outer layer is called the pericardium.


The histological section shows the inner layer called the endocardium (endo) which lines the inner portion of the cavity and the myocardium (myo) is the middle layer which in this case is relatively thin since it is from the atrium, and then the outer pericardium (peri). 
Ashley Davidoff, M.D.

The layers are complex in their makeup.  The endocardium consists of an endothelial layer which rests on a subendothelial layer and basement membrane.  Between the endocardium and myocardium there is a subendocardial layer. The myocardial layer is complex in the manner in which the myocardial cells are oriented and organized.  The pericardial layer consists of two basic layers between which is the pericardial space, and each of which is made of unique tissue.

The diagram shows the three basic layers of the heart: the endocardium myocardium, and pericardium The endocardium consists of an endothelial layer made of a single layer of squamous cells abutting the cardiac cavity. Below this layer there is a fine network of collagen fibers and a basement membrane. The fine collagen layer and basement membrane together are called the subendothelial layer. The endothelium is anchored by the basement membrane. Below the basement membrane is the subendocardium which consists of dense collagen elastic tissue, capillary network, arterioles, venules, smooth muscle cells and elastic tissue. The maroon tissue below this layer is the myocardium. External to the myocardium is the pericardium which consists of an inner visceral pericardium, (light pink) the pericardial space (yellow), and an outer parietal pericardial layer. The outer parietal pericardium consists of an inner seroelastic layer (dark pink) and an outer fibrous layer (gray). Images courtesy of: Ashley Davidoff, M.D.

Structure of the Heart: Principles

The endocardium consists of a single layer of squamous endothelial cells that rests on a layer of fine collagen fibers and a basement membrane.

The squamous endothelial cells are shaped like the scales of a fish and have oval or round nuclei.  The squamous lining of the entire heart is continuous with the endothelial cells lining all the vessels in the body forming one large sheet of tissue spread throughout the entire cardiovascular system. Perhaps one can think of it as a tubular table cloth that extends from the toes to the head –one long, extensive, and remarkable sheet of tissue.

The endothelium rests on a continuous layer of fine collagen fibers, which is itself anchored by a basement membrane.  These two structures (fine collagen layer and basement membrane) form the subendothelium.  Beneath the subendothelium is a thicker layer of dense connective tissue forming the subendocardium. It is composed of collagen fibers, elastic fibers, smooth muscle cells, small blood vessels, and in the ventricles may contain specialized cardiac muscle cells of the conduction system. The connective tissue in this region binds the endocardium to the myocardium.

The endocardium is variable in thickness, being thickest in the atria (left > right) and thinnest in the ventricles particularly the left ventricle. Localized areas of endocardial thickening (jet lesions) are common, particularly in the atria, as a result of turbulent blood flow within the chamber.

Macroscopically the endothelial surface is shiny, smooth, and moist.

The post mortem specimen reveals the opened the left atrium and a view of the anterior leaflet (al) and the posterior leaflet (pl) of the mitral valve. The patent foramen ovale is shown on the septal side of the left atrium. The glistening surface of the endothelium is seen throughout the LA, extending seamlessly onto the mitral valve. It is seen in cross section (white arrow) as part of the white endocardium, together with a thin myocardial layer (maroon arrow) and pericardial layer (pink arrow).
Ashley Davidoff MD
The left ventricle that has been opened along the ventricular septum shows the septal wall to your left and the free wall with the papillary muscles to your right. Note the glistening endothelium which has a whitish sheen. The myocardium lies directly under the endocardium. Note also the two sets of papillary muscles, and the fibrous continuity of the mitral valve with the aortic valve. A VSD is noted on the superior aspect of the septum.
Ashley Davidoff MD
The reconstructed CT scan shows the thin endocardium (white arrows) throughout the heart – which is in fact one continuous sheet of tissue connected across the whole circulatory system. The thin white layer is seen in the left atrium, left atrial appendage (laa) over the posterior leaflet of the mitral valve (pl), in the left ventricle (LV) and in the right atrium. The surface of the left ventricle, left ventricular outflow tract (lvot) and right atrium are also lined by the endothelium. Images courtesy of: Ashley Davidoff, M.D.

There are certain diseases that cause thickening of the endocardium usually caused by subendocardial ischemia.  Endocardial fibroelastosis (EFE) which is seen in the endocardium of the left ventricle in hypoplastic left heart syndrome is shown below.  The entity is thought to result from ischemic changes induced by the suprasystemic pressures in the left ventricle caused by severe left ventricular outflow obstruction and resulting in subendocardial ischemia and secondary fibrosis.

The gross pathology specimen is a case of hypoplastic left heart with aortic stenosis and mitral stenosis, revealing a thickened endocardium with left ventricular hypertrophy and deformed and thickened mitral valve and papillary muscles. The thickened endocardium is caused by the high pressures generated in the LV causing subendocardial ischemia and resulting in a condition called endocardial fibroelastosis (EFE). Images courtesy of: Ashley Davidoff, M.D.

Principles : Myocardium

The myocardium is made up of layers of cardiac myocytes (75% of the total volume of the myocardium), attached to each other by connective tissue fibers, and arranged in spiral bundles. The myocardium is the contractile layer of the heart and hence the major function of myocardial muscle cells is to execute the cardiac contraction-relaxation cycle.  The cell is striated, with a single nucleus, with dark staining intercalated discs.  It is thickest in the left ventricle and thinnest in the atria.  The overall architecture is one of muscles arranged in spiral and circular bundles.

A drawing of the histology of the myocytes of the heart showing how they are connected and related as a continuum enabling a coordinated contraction pattern. Note that the cell membranes are interrupted allowing the cells to freely communicate with each other. This arrangement is called a syncytium – an open door approach of the cells to allow efficient communication and connection.
Ashley Davidoff MD
The myocytes tend to be long, thin, and slightly rectangular. The nuclei are round and blue. Connective tissue between the muscle cells is seen as a pale pink, collagenous material in which parts of blood vessels can be seen. Courtesy of: Ashley Davidoff, M.D.


Principles : Ventricular Myocytes

The muscles of the ventricles are arranged as:

(1) external longitudinal layer

(2) middle circular and

(3) inner longitudinal layer.

Isolated bundles of cardiac muscles project into the lumen of the ventricle forming the trabeculae carneae.

The overall architecture of the myocardium of the left ventricle is in the form of a figure of 8 with one side attached to the subendocardium and then a gradual helical twist, almost to 180 degrees as it extends to the subepicardial surface.

A myofiber or myocyte is the basic structural and functional unit of the myocardium.  The cells are held together by surrounding collagenous, connective tissue with strands of collagen also connecting the myofibers to each other.  Within the myofiber there are myofibrils.

Principles : Pericardium

The pericardium consists of two basic layers.  There is an inner layer called the visceral pericardium that is made of a layer of fibroelastic connective tissue, blood vessels, lymphatics, nerve fibers, and a variable amount of adipose tissue that merges with the myocardium.  The second layer called the parietal pericardium is a more superficial layer, and is made up of a tougher fibroelastic layer, called the fibrous pericardium and a more delicate mesothelial, serous lining.

 Visceral Pericardium

The epicardium (or visceral pericardium) forms the outer covering of the heart. (Cormack).   Its free surface is composed of a single layer of flat to cuboidal mesothelial cells, resting on a layer of connective tissue rich in elastic fibers.  The subepicardial space adjacent to the myocardium contains blood vessels, nerves and an abundance of fat cells.

 Parietal Pericardium

The parietal pericardium has two parts: an inner portion that has a serous lining and an outer fibrous component.  The latter is made from collagen with a small amount of elastin.  The collagen is organized in a criss-cross pattern.

When the inner, single cell, thick, cuboidal, mesothelial surface of the linings of both the parietal and visceral pericardium are reviewed under the electron microscope, they reveal microvilli and long cilia which secrete fluid and provide a low friction surface.

Below the mesothelial epithelia a layer of elastic fibrils supports the epithelium.

There is a rich network of lymphatics that provide the substrate for the pericardial fluid.

Quiz Me

What cell type results in the contractility of the heart?
(Note: You will be given 2 tries to answer this question, then the answer will be provided.)

Structure of the Heart: Fibrous Skeleton

The fibrous skeleton of the heart, formed of connective tissue, separates the atria from the ventricles and includes the annuli fibrosi – (rings of dense connective tissue around the valves), trigona fibrosi (masses of  fibrous connective tissue connecting the annuli) and the septum membranaceum (membranous spot at the top of the interventricular septum). It is composed of dense collagen fibers, scattered elastic fibers and occasional fat cells (less regular than tendon, more regular than dermis). The cardiac skeleton serves as the place of origin and attachment of muscles of the atria and ventricles.

Structure of the Heart: Valve Leaflets

Valve leaflets are composed of three layers (ventricularis, fibrosa and spongiosa) and two general cell types (1) endothelium – non thrombogenic external lining and (2) valvular interstitial cells  – heterogeneous cell population composed of fibroblast and smooth muscle cells.  The cardiac valves are lined with endothelium and all have a similar layered architecture consisting predominantly of a dense collagenous core, and the fibrosa layer, close to the outflow surface and continuous with the valvular supporting structures. Towards the ventricular/atrial cavity the ventricualis/atrialis layer is found and it is rich in elastin. Between these two layers is the centrally located core of loose connective tissue, the spongiosa layer. The collagen of the fibrosa layer is responsible for the mechanical strength of the valve, whereas the connective tissue of the spongiosa layer works as a shock-absorber. Normal leaflets and cusps have only scant blood vessels and are avascular structures.

There are three layers of collagen within the valve. The first image (top) shows the fibrosa layer on the aortic side of the valve (pink). This layer consists of radially oriented fibers extending from commissure to commissure. It has a corrugated form enabling it to stretch during systole. The second middle layer is called the spongiosa green and its fibers extend at right angles to the fibers of the fibrosa. On the ventricular side in the third image a cross section of the histological makeup of the aortic valve is shown with the upper layer being on the aortic side and the yellow layer of ventricularis is shown.
Ashley Davidoff MD

Structure of the Heart: Histology of the Cardiac Conduction System

The conduction system is made of myocardial fibers designed for rhythm rather than contraction. They include the nodal cells (AV nodal, SA nodal) and the AV bundle along with its branches (Purkinje cells).

Nodal Cells:  Nodal cells are smaller than ordinary cardiac myocytes, contain fewer and poorly organized myofibrils and no intercalated discs.

Purkinje cells:  They are specialized myocytes found in the subendocardium of the ventricles.  Purkinje cells are rich in glycogen and mitochondria and often have two more nuclei centrally placed.

Quiz Me

Select the tissue layer responsible for the mechanical strength of a valve.
(Note: You will be given 2 tries to answer this question, then the answer will be provided.)
Collagen of the fibrosa layer
Connective tissue of the Spongiosa
Purkinje cells


The macroscopic appearance of the heart follows, with attention paid to the elements that allow the pathologist, clinician, cardiologist, radiologist and surgeon to evaluate the heart.

The universal structural descriptors that are used by all professionals who analyze structure include the size, shape, position and character, as well as evaluation of the connections that enable integration into the body.


Size is one of the most important descriptors of the heart.   It is a measurable entity, and determining whether the heart is normal or abnormal can be verified against a normal standard.   Size and weight of many organs differ between the sexes and among age groups, and it is no different for the heart.  Measurements may be linear, and portray a volume, mass, rate or frequency.  Size may be reflected as a ratio, such as the size of the left atrium and the base of the aorta that should have close to a 1:1 ratio.

The analogy of the heart being fist-sized is helpful conceptually, but has limited use in the clinical realm.  The evaluation of the size of the heart in clinical medicine is of the utmost importance.  Although the global size of the heart is important, the size of the individual chambers is even more so, and in fact essential.

Size of the heart is one of the key determinants in the diagnosis of heart disease.  Each of the chambers is so unique that separate criteria have been developed for each of the chambers.  Linear measurements are still the standard for most evaluations.

Anatomy of the Heart: Anatomical Evaluation

The post-mortem evaluation of the heart historically, has been the manner in which the measurements of the heart evolved, but cannot be accurately transposed to the living and beating heart that is filled with blood and interstitial fluid.

The adult heart measures about 12 cm in length by 8 to 9 cm in width at the broadest part, by approximately 6 cm in thickness. Translated into inches, it would approximate 4.5 by 3.5 by 2.5. The weight of the heart varies from 280 to 340 grams in the adult male and from 230 to 280 grams in the adult female. Thus, for the adult male it is just over half a pound and for the adult female it is about half a pound.

At post-mortem LV thickness of the adult heart ranges from about 8mms to 1.3cms and is usually less than 1.5cms.  The RV wall thickness ranges from 4 mm-8mms., being thinnest on its free wall.

The volumes of the left ventricle have been well studied.  The left ventricular end diastolic volume ranges from 55ccs to 190ccs, and end systolic volume from about 15 ccs to 70 ccs with a stroke volume of 35-130 ccs, and ejection fraction ranging from 55% to 75%.  For males, the volumes are slightly higher and for females slightly lower.

The heart increases in weight and size as human’s age. At birth, the heart appears large in proportion to the diameter of the chest cavity. Between puberty and 25 years of age the heart attains its adult shape and weight. The size of the heart is governed by its overall mass, which reflects ventricular thickness, as well as the volume of the cavities.

This anatomic specimen shows the LV with septal side to the left and free wall side to the right. Note the relatively smooth walled septal surface and the papillary muscle apparatus attached to the free wall side. The thickness of the anterior, lateral, and posterior wall is equal and symmetrical, and although the thickness of the septum is not visible in this view, its thickness approximates the thickness of the other walls. The left ventricular wall thickness is normal and was less than 15 mms.
Ashley Davidoff MD
The free wall in this normal post mortem specimen has been opened, exposing the septum to the right of the image (orange), the tricuspid valve to the left (pink), the RVOT (light blue) and pulmonary valve (purple) superiorly and the moderator band inferiorly. The right ventricular free wall (dark green) is relatively thin and the normal range of thickness is between 4-8mm. In this instance the thickness of the free wall next to the ruler was not more than 5 mms.
Ashley Davidoff MD

Principles in Disease

Tubular structures remain normal in size if the pressure, volume, flow, and integrity of the walls are maintained.  The heart is in effect a tube with modifications and therefore will follow the principles that govern tubular function.

In general tubular structures enlarge as a result of:

increased pressure
increased volume
turbulent flow
loss of wall integrity

Enlargement of the heart may result from hypertrophy or dilatation.  Hypertrophy is caused by increased pressure and it usually results from stenotic valves, or increased afterload as a result of hypertension.

The post mortem specimen shows a short axis transverse view through the right and left ventricle showing hypertrophy of the left ventricle. The ventricular septum measures about 2cms and should normally be less than 15mm. The right ventricle in this view is crescentic in shape with a wall that is normal in thickness.
Ashley Davidoff MD

Increased volume is caused by an increased preload.  An incompetent aortic valve, left to right shunt or a failing heart that cannot pump out what it receives will result in an increased preload.  Loss of structural integrity, caused by a myocardial infarct for example will cause a dilated heart for multiple reasons.  The weakened tissue will bulge, and the accumulation of blood in the chambers as a result of a failing pump may both contribute to the enlargement.

Dilated Left and Right Ventricle
Complex Size Changes with Disease
Atrophy Caused by Old Infarction, Swelling with New Infarction,  Compensatory Hypertrophy and Normal
This pathological specimen shows a short axis through the heart with the left ventricle (right of image) and the right ventricle (left of the image). The free wall of the left ventricle contains the papillary muscles and is slightly thickened either as compensation to the remaining diseased myocardium or due to other comorbid diseases such as hypertension or aortic stenosis. There is a fresh infarction (black) posteriorly in the left ventricle extending to the posterior wall of the RV as well. The septum is thinned and fibrotic from an old infarction. The anterior wall of the right ventricle is hypertrophied.
Ashley Davidoff MD

Causes of a small heart are much less common, though smallness of individual structures such as stenotic valves, hypoplasia, aplasia, and dysplasia commonly occur in the congenital disorders of the heart.  There are usually compensatory mechanisms in the heart that will attempt to overcome the deficiency so that the overall size of the heart increases.  For example, in tricuspid hypoplasia or atresia, the right atrium will enlarge as it attempts to push blood through the narrowed tricuspid valve, so that the overall size of the heart may increase to the extent that the child presents with a gigantic heart caused by a very dilated right atrium.

When the heart enlarges in disease, the cause of the enlargement can be approached in many ways. An anatomical differential diagnosis is one place to start.  First, the parts of the structure being analyzed must be identified.  Next, the enlargement should be localized to one or more of the components of the heart.  If a heart is enlarged on a chest X-ray an important branch point depends on determining whether the left side is abnormally big, the right side or both.  Left-sided enlargement allows deduction that the left atrium and or left ventricle is enlarged.  If it is finally established that the left ventricle is normal and the left atrium is enlarged, then stenosis of the mitral valve becomes the most likely candidate for the cause of the disease.  Since mitral stenosis in an adult is almost always caused by rheumatic fever, one can further deduce that the cause of mitral stenosis was a pediatric infection with Lancefield type A beta hemolytic streptococcus bacteria.  The patient probably acquired cardiac involvement from streptococcus pharyngitis when he or she was between 5-15 years.  The polymers in the wall of the organism, called M proteins, are highly antigenic and at the time forced the patient’s defense mechanism to create antibodies.  While responding to the foreign organism, these antibodies also inadvertently reacted to the patients own tissues, including the myocardium, and or mitral valve, and possibly the pericardium, brain and even joints.  The depth of the detail in the diagnosis depends on the physician’s knowledge, but the story would not have been a story, and the diagnosis would not have been made, and treatment would not have been instituted, had a diagnostic finding not been identified – in this case the change in size of the heart.   The beginning of diagnosis, even if it involves complex disease, starts with simple observations of aberrant structure or function.  In this case it started with the simple observation of a change in size in the heart.

Two different patients showing the normal patient on the left and the CXR of a patient with an enlarged triangular shaped heart on the right. The triangular heart with upturned apex is characteristic of right ventricular enlargement, and the elevation of the carina and a double density seen on the right side of the heart suggests left atrial enlargement. These findings are consistent with rheumatic mitral stenosis.
Ashley Davidoff MD

Clinical Medicine

In clinical medicine palpation of the heart is the most valuable tool to assess heart size.  Most of the right ventricle is positioned anteriorly while only a small portion of the left ventricle, dominantly the apex, is anterior.  The position of the apex enables the assessment of left ventricular size.  It is normally palpated with the tips of the index and middle fingers in the midclavicular line in the 5th intercostal space.  In left ventricular enlargement the apex is projected down and out (laterally).  The right ventricle lies anteriorly and is not usually felt but when enlarged a prominent parasternal heave is felt with the palm of the hand.

Clinical Medicine: EKG

EKG is better able to evaluate individual chamber enlargement with atrial evaluation identified in the p wave and ventricular enlargement evaluated in the QRS complex.  Right-sided structures are evaluated in the leads overlying the right side of the heart, and left sided enlargement similarly on the leads on the left side of the heart. When the right atrium is enlarged the p wave becomes enlarged.  The characteristic  “p pulmonale” characterized by a high amplitude, (greater than 2.5mm) peaked, and narrowed p wave is present.  When the left atrium enlarges the p wave, “p mitrale” results which is broader (>.11 msecs) and notched so that the shape of the wave becomes shaped like an “M’ .  Right ventricular hypertrophy is characterized by an R wave in leads V1 > 7mm, or if the R wave is larger than the T wave in V1.  Right axis deviation is also a sign of right ventricular dominance.

Left ventricular hypertrophy has a number of criteria:

      • QRS height
      • R in lead I plus S in lead III greater than 25 mm.
      • Increased precordial QRS voltage: S in lead V1 plus R in either V5 or V6 greater than 35 mm.
      • Large leftward voltage: R wave in lead L greater than 11 mm.
      • Typical ST and T abnormalities:
        • ST depression or T wave inversion (or both) in the “lateral” leads (I, L, V4-V6)

Clinical Medicine: Imaging

There are a wide range of technologies that are able to measure cardiac size with variable accuracy.  The CXR was the first imaging technique to evaluate heart size and was the only imaging technique for about 70 years until modern technology evolved.  It is still commonly used but is not as accurate as echo CT or MRI.

Imaging: Chest Radiograph (CXR)

The cardiothoracic ratio is the ratio between the transverse diameter of the heart and the widest diameter of the chest.  The normal cardiothoracic ratio is less than 50%.

This CXR is of historical interest showing the manner in which cardiomegaly was assessed using the cardiothoracic ratio before the era of echocardiography and advanced imaging. The transverse dimension of the heart was measured to the left and right of midline using the maximum diameter. In this instance the dimension to the right of midline was 3cms and to the left it was 10.2cms giving a total of 13.2cms. The maximum dimension of the chest from inner ribs to inner ribs was 28.2cms. The cardiothoracic ratio was therefore less than 50% (13.2/28.2) and thus considered normal.
Ashley Davidoff MD

The actual measurement of the cardiothoracic ratio is not used in clinical practice, but a gestalt of the approximate cardiothoracic ratio is commonly used.  The distinction between lung disease and heart disease for example in a patient with shortness of breath may rest in identifying cardiomegaly.  The A-P examination magnifies the heart so evaluation of cardiomegaly with this projection should be used with caution.

In the P-A projection the normal heart takes up about 30% of the diaphragmatic surface. Similarly in the lateral projection the heart takes up a third of the diaphragmatic surface. In addition the heart takes up the bottom 1/3 of the retrosternal air space.
Ashley Davidoff MD

Imaging: Applied Anatomy

In order to fully evaluate heart size on the chest X-ray (and any other imaging technology for that matter) knowledge of the relative position of the structures is important.  A useful overlay is shown below.

If we were to “crack open” the chest of the chest X-ray, the structures that would dominate this bloody, black and white scene, would be the right sided chambers. The right ventricle (RV) would be the dominant anterior chamber, and would form the dominant interface with the diaphragm. The right atrium (RA) would form the border with the right lung. The RA would of course be slightly posterior to the RV. The left border would be formed by the left ventricle. Most the left ventricle is hidden posteriorly in this view. The left anterior descending artery would be visible from this anterior view. It marks the position of the interventricular septum.
Ashley Davidoff MD
The lateral chest examination reveals an overlay of the structures that are visible, with the right ventricle (triangular blue structure) being anterior giving rise to the pulmonary outflow tract. The heart occupies the bottom 1/3 of the length of the sternum, with the upper 2/3 being occupied by lung (black tissue) The left ventricle is posterior and inferior occupying the lower 2/3 of the posterior border of the heart. The left atrium forms the upper 1/3 of the posterior border. Note the relationship of the IVC with the left ventricle. At the cardiophrenic angle posteriorly, the IVC forms the border and not the LV. When the RV enlarges it starts to occupy more than 1/3 of the retrosternal space. When the LV enlarges it pushes posteriorly and down so that the posterior border of the heart at the posterior cardiophrenic region is occupied by the LV and not the IVC, and when the LA enlarges it also pushes posteriorly on the esophagus as well as the left main stem bronchus (not shown).
Ashley Davidoff MD

Imaging: Echocardiogram

The echocardiogram provides a real time, safe, accurate, and relatively inexpensive method of evaluating the structures of the heart at any phase of the cycle.  Measurements of size including volume, ejection fraction, wall thickness, valve areas, velocity and direction of flow are relatively easy to measure.  This technique is the bread and butter of structural cardiac evaluation.

This grayscale apical long axis view of the heart demonstrates the normal left ventricle (LV), aortic valve (AoV), aortic root (Ao), and left atrium (LA).


This side-by-side image demonstrates the grayscale image on the left and the color image on the right showing inflow from the left atrium (blue) and outflow from the left ventricle into the aorta (orange) . Image compliments of Philips Healthcare, Bothell, WA 

Due to the real-time nature of sonography and the echocardiographic examination, the clinician is able to observe the flow through the normal and abnormal heart.

This grayscale echo of the heart shows the left ventricle, anterior (light pink) and posterior leaflets of the mitral valve, the aortic valve (dark pink), and the base of the aorta. There is a focal thickening of the ventricular septum (green) in the left ventricular outflow tract just proximal to the aortic valve. The region is also slightly more echogenic than the remaining myocardium (maroon). This case demonstrates a case of asymmetric septal hypertrophy or muscular subaortic stenosis.
Ashley Davidoff MD

Imaging: Computerized Tomography (CT)

CT scan is not used routinely for imaging of the heart because it is not real time, is expensive, requires gating for accurate measurements, requires contrast injection, and involves radiation exposure.  On the other hand it is used routinely for examinations of the chest, and although this examination is not tailored for cardiac evaluation, evaluation of the size and an estimate  of the thickness of component structures is possible.

Volume measurements and wall thickness measurements requires a diastolic frame in order to standardize the measurement and also because there is thickening of the myocardium during systole as it shortens. This requires a gated study in order to determine the phase of the heart

However, the size of the atria and to some extent the ventricles can be fairly accurately and subjectively assessed often by reviewing the shape of the chambers.

The axial gated CT scan through the right and left ventricle at end diastole shows the normal size and shape of the right ventricular inflow tract and left ventricle. The right ventricular inflow (underlying the RV measurement)  looks smaller than the LV in volume, in this view, since essentially it makes up for the volume in its second “floor” which sits more cranially as the right ventricular outflow tract. The left ventricle only has a single level or floor. Thus in this view the RV looks and measures smaller then the LV. Note also that the apex of the left ventricle protrudes slightly more anteriorly than the RV even though it is the posterior ventricle, because it is the chamber that forms the apex of the heart. The septum also bulges toward the right ventricle due to the higher pressure in the left ventricle. Courtesy of: Ashley Davidoff, MD
This elderly patient had sustained a cardiac arrest just 24 hours prior to the examination and the CT shows a bulbous and dilated left ventricle. Both the shape and the size of the LV cavity are clues to the enlargement of this heart. A small posterior pericardial effusion is present. Courtesy of: Ashley Davidoff, M.D.

Imaging: Magnetic Resonance Imaging (MRI)

MRI is not a routine method for the evaluation of heart size due to the accurate capabilities of echocardiography which is safe, inexpensive and accurate.  However, there are many advantages that gated cardiac MRI offers in the evaluation of the heart.

In the gated MRI, systole and diastole can be differentiated and so standard measurement to thickness and volume can be applied, for evaluation of size. This MRI series demonstrates the heart in systole and diastole. Image 1 demonstrates ventricular systole. The atrial chambers are full, the A-V valves are closed and the ventricular chambers are contracted. Image 3 is a color overlay of the closed A-V valves of image 1. Image 2 demonstrates ventricular diastole. The atrial chambers are emptying, the A-V valves are open and the ventricular chambers are full. Image 4 is a color overlay of the open A-V valves of image 2. Courtesy of: Philips Healthcare
The coronal non gated T1-weighted MRI through the left ventricle shows a thickened left ventricle due to the hypertension associated with coarctation. Even although the study is non gated, the thickness of the LV is excessive, even for a systolic frame. Courtesy of: Ashley Davidoff, M.D.

Imaging: Angiography

Overall heart size is not easily evaluated by angiography since only the cavity is visible.  However, the hypercontractile ventricle is an indirect sign of ventricular hypertrophy.

The normal ventriculogram in the RAO projection is demonstrated in image a and overlaid in c, while the hypercontractile LV, caused by aortic stenosis, manifests with a ballet slipper like appearance of the LV at end systole (image b and d). The ejection fraction of the left ventricle, in the patient with aortic stenosis, was 80%. The aortic valve is mildly thickened and has minimal doming (green overlay). Courtesy of: Ashley Davidoff, M.D.

Imaging: Clinical Examples

The series of a plain film of the chest (a), and coronal image of a reconstructed CT (b), reveals an almost wall to wall heart called a cor bovinum – literally a bull’s heart – corresponding to its very large size. The axial image c, shows a calcified mitral valve (red arrow) consistent with mitral stenosis, secondary left atrial enlargement (LA in c), pulmonary hypertension (large main pulmonary artery – blue arrow)  and an extremely dilated right atrium (RA in a, b, c and d). Courtesy of: Ashley Davidoff, M.D
These three images represent T1 weighted images of the RV reflecting from left to right: normal, dilated, and hypertrophied conditions. Normal thin-walled capacious RV is the first image on the left with a thin wall and triangular shape. The middle image is from a patient with an atrial septal defect (ASD) resulting in a volume overloaded, thin-walled, rounded, and dilated RV . The image on the right is from a patient with congenital heart disease with pressure overload of the right ventricle showing heavy trabeculations of the RV and thickened wall.
Courtesy of: Ashley Davidoff, M.D
What is the cause of the cardiomegaly? The CT scan is from a 76 year old man in whom the dominant finding is of left ventricular enlargement, characterized by the rotund shape of the ventricle. The RA and RV are also enlarged based on this image, and LA was enlarged as well suggesting global cardiomegaly consistent with a cardiomyopathy. The clue to the cause of the enlargement is the segmental nature of the disease, characterized by the asymmetry thickness when the free wall thickness is compared to that of the thinning of the septum. In addition, the presence of fat (yellow overlay) in the thinned and probably scarred myocardium, makes ischemic cardiomyopathy the likely diagnosis.
Courtesy of: Ashley Davidoff, M.D
The CT of this patient shows a severe pectus excavatum causing compression of the right atrium, left atrium and right ventricle. Note the right sided breast prosthesis. Pectus excavatum does not usually affect the function of the heart. All images courtesy of: Ashley Davidoff, M.D.
These images represent the left ventricular outflow tract (LVOT) and apical four chamber views obtained during an echocardiogram. The patient is suffering from cardiac failure as a result of dilated cardiomyopathy. All four chambers are dilated and appear full and distended. Image courtesy: Philips Healthcare


The normal four chamber heart


A heart demonstrating hypertrophic cardiomyopathy
Compare the current case of a dilated cardiomyopathy heart to the hypertrophic and normal four chamber heart view. Images courtesy of Philips Healthcare, Bothell, WA.

Clinical Medicine: Shape

The shape of the heart is quite complex and can be described in many ways based on which professional is evaluating the heart and from which angle it is viewed. The shape is of extreme importance in imaging since a subtle change may be the key to the diagnosis.  Right ventricular dysplasia, for example can cause life threatening arrhythmias and sometimes, the only clue to the diagnosis is a subtle bulge of the right ventricular outflow tract.  Thus although simple in concept, shape of structure is a key element to diagnosis.

The shape of the heart has been variably described as conical, triangular and ovoid.  It is rather difficult to provide a single descriptor that accurately describes the shape of the heart mostly because of the variety of facets or angles from which  it can be evaluated.

The artistic rendition of the heart attempts to reveal the ambivalence in the shape of the heart as either a triangular structure or an oval on its side, and it seems to satisfy both shapes in this view. The right ventricle dominates the anterior view and the left ventricle peeks around the left border of the heart holding its power as its trump card behind the right ventricle. Courtesy Ashley Davidoff, M.D.

The anatomist, and pathologist will have a sense of the shape with the heart devoid of life and blood while the surgeon and the imager will have a different perspective with a heart filled with life and blood that changes in shape every millisecond.  On the other hand the detail of muscle bundles, chordae, as well as either micro components are part of the secrets of the heart available only to the anatomist and pathologist, but not yet visible to the imager at this time.

The angle from which the heart is viewed also affects the perspective.  The frontal view is different from the lateral which will be different from all the other projections that are used to view this organ including the oblique, coronal, long axis, and short axis.  In each of these many views the shape will invoke different subjective descriptions, and most importantly will help define whether the heart is normal or not.

Each of the chambers is quite unique in individual structural characteristics and shape is no exception.    The first general description will relate to the anatomical view- how it appears to anatomist or pathologist.

The post mortem view of the heart in the chest cavity shows a horizontal orientation of the heart, since the lungs are deflated the heart is more horizontally oriented and has an almost rectangular shape with the longest axis from right to left. The anterior view is dominated by the right ventricle which tends to be triangular. The inferior border of the heart is straight while the rightward, superior and leftward borders are minimally rounded. Courtesy pf: Ashley Davidoff, M.D.

The overall external surface is smooth.

The shapes on the inner surface of the heart are unique to each chamber.  The right atrium has a combination of smooth areas, with both large and smaller muscular bundles; the left atrium is mostly smooth, while the left ventricle is smooth but for its set of papillary muscles, and the right ventricle tends to be heavily trabeculated.

Shape: Clinical and Imaging

The shape of the heart cannot be evaluated by clinical examination. However, in imaging it is a key and major factor in diagnosis.

In vivo, during life, the heart on a chest X-ray is usually imaged during inspiration and the heart tends to be more elongated.

The normal heart lies as a gracile structure in the middle of the chest and takes up about 25% of the chest volume. Its shape in this view is interpreted by some as being more or less triangular with the base on the diaphragm and apex in the superior mediastinum. At its base on the diaphragm, the left ventricular apex is tipped a little more inferiorly than the right side. It does differ among individuals. Also if a patient does not take a deep breath, then the heart becomes more horizontal in orientation. Courtesy of: Ashley Davidoff, M.D.

Others perceive the overall shape in this view as an oblong, perhaps an egg on its side, or a football waiting to be punted.

The shape of the heart in this view could also be interpreted as an oval on its side and for some viewers this makes sense, with the inferior aspect pointing down and to the left and the other superiorly and right. Courtesy of: Ashley Davidoff, M.D.

The perception as to whether the heart is shaped like a  triangle or an oval depend on multiple variables including the viewers perception, the phase of the respiration, the body habitus of the patient and the overall structure of the individual heart.

In truth though, the heart has both triangular and ovoid features.  The right ventricle tends to be triangular and the left ventricle more oval, and this theme will be revisited a number of times throughout this module.

This is an external and frontal view of the heart. The vessel that you see coursing straight down the center of the heart is the left anterior descending artery, (LAD) that runs anterior to the ventricular septum in the interventricular groove (vertical limb of the cross) separating the right and left ventricles. Conceptualize the triangular shape of the right ventricle, and the ovoid almost football shape of the left ventricle.
Courtesy of: Ashley Davidoff, M.D.
The left ventricle is shaped like a football or if you are of British or British Commonwealth origin you would call it a rugby ball – perched ready for kick-off.
Courtesy of: Ashley Davidoff, M.D.
The right ventricle is less sporty in its shape. It is triangular and would do better in a percussion band than on a football field.
Courtesy of: Ashley Davidoff, M.D.
The CT scan of the heart has been reconstructed in the coronal view with image (a) being slightly anterior to image b. In image a, the triangular nature of the RV is noted and in image b the ovoid nature of the LV is noted. All images courtesy of: Ashley Davidoff, M.D.

The CXR and EKG used to be standard and first line methods of evaluation of the heart.  The shape of the heart on CXR was a means of evaluating its size.  Although it is still important, and practical, it is subjective.   The enlarged right ventricle is reflected in triangular cardiomediastinal silhouette while the enlarged  left ventricle  is reflected as an ovoid shape on the frontal view.

Two different patients showing the normal patient on the left and the CXR of a patient with an enlarged triangular shaped heart on the right. The triangular heart with upturned apex is characteristic of right ventricular enlargement, and the elevation of the carina and a double density seen on the right side of the heart suggests left atrial enlargement. These findings are consistent with rheumatic mitral stenosis. 
All images courtesy of: Ashley Davidoff, M.D.

Clinical and Imaging: Shapes of the Heart in Congenital Heart Disease

A coronal view of the heart as viewed by CT or MRI imaging portrays the deeper coronal shapes of the heart, its muscle and cavities.  In these views the triangle of the RV and the oval of the LV are maintained.

The collage of frontal views of the heart is a combination of images from a personal collection and borrowed from the internet for educational purposes only. From top left and across the rows they are: the normal heart , the “football” of LV enlargement, the “triangle” or “proud breast” of RV enlargement, “snowman” of total anomalous pulmonary venous return, the big mogul of skiing down the left heart border in pulmonary stenosis or pulmonary hypertension,  “egg on its side” of D transposition of the great vessels, “boot shaped” heart seen in both pulmonary atresia and Tetralogy of Fallot, the long smooth mogul that has a differential diagnosis of L transposition, absence of the pericardium, and juxtaposition of the atrial appendages, the box shaped large heart of Ebstein’s anomaly, the D loop where the genetic instruction of keep right ” seems likely, and the water bottle” heart of a large pericardial effusion. Courtesy of: Ashley Davidoff, M.D.

Clinical Medicine: Axial Imaging

In this projection the triangular nature of the RV is mostly retained, but because of the non orthogonal nature of routine cross sectional imaging, the apex of the LV is not usually imaged orthogonally, so the oval appearance of the LV is not consistent. The shape of the atria are best defined and assessed in the axial projection.

The Atria

In the axial projection the atria have flattened free borders- the lateral border of the right atrium and the posterior border of the left atrium.  When it enlarges the borders become rotund indicating an increase in pressure or volume.

This axial image of the heart is through the right atrium and left atrium which are normal and about the same size. The left ventricle with the papillary muscles and the right ventricle with its papillary muscle are well seen and in this view both have a triangular shape. Note that the normal atria have flattened outside walls. Courtesy pf: Ashley Davidoff, M.D.
Both the right atrium and left atrium in this axial CT study are enlarged. Not only is their absolute size increased, as witnessed by the less than 1:1 ratio of the aorta to the LA, but the outer borders of both atria are rotund instead of being flat. Courtesy of: Ashley Davidoff, M.D.
An aneurysm of the left ventricular apex is a common occurrence and is recognized by both a change in shape and size of the apex. These changes are accentuated in systole but in the non gated study as shown below, the abnormal size and shape are easy to recognize. Courtesy of: Ashley Davidoff, M.D.

Clinical Medicine: Position

The heart lies between the lungs in the middle mediastinum and is enclosed in the pericardium. It is placed obliquely in the chest behind the body of the sternum and adjoining parts of the rib cartilages, and projects farther into the left than into the right half of the thoracic cavity. About one-third of it is situated on the right and two-thirds on the left of the median plane. Boundaries of the heart are clinically important as an aid in diagnosing heart disorders.

The heart lies within the chest cavity slightly to left of midline, in the lower 2/3, and rests on the diaphragm. Courtesy of: Ashley Davidoff, M.D.

The heart does not lie upright with atrial chambers totally superiorly.  Rather it is tipped with the atria rightward and backward and ventricles leftward and forward.   In addition, the right sided chambers are more anterior and superior than the left sided chambers. It is of extreme importance for you to spend some time on this section trying to visualize in your mind’s eye how the heart lies, since once the template is captured, you can turn the heart in any which way and you will be able to find your way around it.

The heart chambers do not lie in a completely vertical orientation. The atria are rightward, superior and posterior to the ventricles. The right sided structures are anterior and superior to the left sided structures. Courtesy of: Ashley Davidoff, M.D.


The relevance of the anatomy is introduced in the evaluation of the chest X-ray.

The right ventricle is anterior to the left ventricle and is also superior. The right atrium (blue ring overlay) is slightly superior and anterior to the LA i.e. blue right sided structures are superior and more anterior than red left sided structures . The atria are superior and posterior to the ventricles as shown in the diagram.
Ashley Davidoff MD

The cross-sectional images from a CT scan through all 4 chambers reveals the relative position of the chambers and A-V valves. In general “blue” chambers are both anterior to and superior to the “red” chambers so that both the right atrium (RA) and right ventricle (RV) are anterior to the LA and LV. The tricuspid valve (blue valve) follows the rule and is slightly anterior to the mitral valve as well. Not shown here is that the fact that the right sided structures are slightly superiorly positioned. Images courtesy of: Ashley Davidoff, M.D.

Position: Embryologic Considerations in Positioning of Cardiac Structures

The fetal heart begins beating at 22 to 23 days. The position of the heart in the chest, and the position of the chambers are defined in the embryological development of the heart.

There are 4 major events in embryology of the heart.

Situs development
Growth and regression

Positioning of the apex is a minor independent event separate from situs and looping.

Of these events situs, looping, and apex positioning play a major role in the positioning of the heart and its components.

Innate in the genetic instruction is positioning of the atria, lungs, tracheobronchial tree and some of the abdominal organs.  Normal situs instruction would result in the positioning of the right atrium on the right, left atrium on the left, right lung, liver, pancreatic head, and gallbladder on the right, and left lung, spleen, and pancreatic tail on the left.

Looping of the heart is also under genetic instruction, and normal looping would bring the right ventricle to the right and left ventricle to the left.  This usually places the aorta to the right of the pulmonary artery.

Positioning of the apex is an independent event and is usually the result of the final positioning of the left ventricle.

Position: Levocardia

Levocardia is the normal positioning of the heart dominantly in the left chest as a result of the normal placement of the apex by the left ventricle

Normally positioned apex – as a result of a D loop and settling of the apex into the left chest, as its final position.
Ashley Davidoff MD
Axial view of the fetal heart through the chest demonstrating the normal orientation (levocardia). Image courtesy of Philips Healthcare

Position: Dextrocardia

Dextrocardia is defined as a malposition of the heart that can be congenital or acquired resulting in the apex of the heart being in the right chest.  There are two congenital forms; one is associated with situs solitus, and the second associated with situs inversus.  The form that is associated with situs solitus is thought to be due to an embryonic arrest resulting in the right ventricle (rather than the left) forming the apex.  In this instance the right ventricle is still on the right side and the left ventricle is on the left side.  This form of dextrocardia is associated with a higher incidence of congenital abnormalities.  The second form of the congenital version is associated with situs inversus. In this situation the incidence of associated congenital abnormalities is lower. Mesocardia is also an atypical position, with the heart in a central position in the thorax; neither a right nor leftward pointing apex.

Acquired dextrocardia may be due to either loss of volume in the right chest or a push due to mass effect from the left side.

The PA chest X-ray shows the apex pointing rightward and most of the heart is in the right chest. Note also that the stomach bubble is in normal position, and so situs solitus is present. This is a case of isolated dextrocardia, caused by an arrest of development, and not associated with situs inversus, but subject to a higher incidence of other congenital anomalies.
Ashley Davidoff, M.D.
The CT is from an elderly patient with dextrocardia and situs solitus. The scout film before the CT shows dextrocardia and Harrington rods are noted in the thoracic spine. Image b, shows the apex of the heart pointing to the right.
Ashley Davidoff, M.D.
The CXR and bronchogram is from a 30-year-old male who presents with a long standing history of a productive cough, sinus headaches, and infertility. The bronchogram shows inversion of the bronchi with the long thin bronchus characteristic of the left bronchus being right sided and short “fat ” bronchus characteristic of the right being left sided. Situs inversus and dextrocardia exist. However the history of sinusitis and infertility make the diagnosis of Kartagener’s syndrome likely.
Ashley Davidoff, M.D.
The series of CT scans show an acquired dextrocardia. In image a, the heart is not seen at all – but since it is not in the left chest, it is presumed to be in the right. The mediastinum as seen by the trachea is shifted to the right and the right lung is shifted across the midline into the left chest. The patient is status post pneumonectomy. Image b shows the heart completely in the right chest, and image c, shows the shift of the left lung across the midline and complete absence of the right lung. Image d confirms situs solitus.
Ashley Davidoff, M.D.
In this case the scout film manifests with what appears to be a case of dextrocardia. Image b shows a slight shift of the heart to the right but the appearance is dominated by a large right atrium and left atrium. Image c confirms the leftward position of the apex and normal relationship of the left apex and right ventricle. Image d shows situs solitus with reflux of contrast into the dilated hepatic veins indicating tricuspid regurgitation. The enlarged right atrium in this case gives the appearance of dextrocardia.
Ashley Davidoff, M.D.
This is a CT scan through the chest in which the apex of the heart points forward. The left ventricle (LV) is left sided and the right ventricle is right sided. There is situs solitus of the atria. This is a case of mesocardia ie neither right nor leftward pointing apex. All images courtesy of: Ashley Davidoff, M.D.
Axial view of a right displaced heart due to a diaphragmatic hernia. Image courtesy of Philips Healthcare.

Position: Situs Inversus

Situs inversus is a congenital disorder in which the organs of the chest and abdomen are inverted in position.  Situs inversus is an abbreviated term for situs inversus viscerum.

The cause of the genetic aberration is usually an autosomal recessive but situs inversus is associated with entities such as the asplenia syndrome, polysplenia syndrome, Kartagener’s syndrome (primary ciliary dyskinesia).

The result of the aberration is either a partial form (situs inversus partialis) or a total form (situs inversus totalis).

Structurally,  situs inversus totalis the atria, tracheobronchial tree, and lungs are inverted, while in the abdomen the  right sided organs including the liver gallbladder, head of the pancreas, and left sided structures such as the spleen, stomach, tail of the pancreas are inverted.

Situs inversus is not necessarily associated with dextrocardia. isolated dextrocardia without situs inversus is associated with a much higher incidence of congenital heart defects.

Functionally, situs inversus in the absence of other congenital defects can be totally asymptomatic, but is usually fatal in asplenia syndrome.  In this entity situs is usually ambiguous.

The  post mortem examination of  an unfortunate baby with severe congenital anomalies including situs inversus totalis, dextrocardia, left sided liver, right sided stomach, severe congenital heart disease, shunt possibly a Blalock Taussig, large right ventricle, and gross pathology position malposition. Note that the right lobe of the liver is on the left, and the stomach is on the right. Courtesy of: Ashley Davidoff, M.D.

     What type of heart orientation does this radiograph demonstrate?
(Note: You will be given 2 tries to answer this question, then the answer will be provided.)

Position: Character

The heart has a smooth, glistening, external surface surrounded by a variable amount of epicardial fat.  It is red to maroon in color, muscular, rubbery, and distensible,  but less so than organs of the gastrointestinal tract. Its inner surface is covered by a smooth white glistening surface endothelium which has an underlying fibrovascular endocardium and subendocardium.

The atria have thin muscular walls, while the ventricles, particularly the left ventricle are much thicker.

The left ventricle that has been opened along the ventricular septum shows the septal wall to your left and the free wall with the papillary muscles to your right. Note the glistening endothelium which has a whitish sheen. The myocardium lies directly under the endocardium. It is lighter red, muscular and rubbery. Note also the two sets of papillary muscles, the fibrous nature of the valves and the fibrous continuity of the mitral valve with the aortic valve. A VSD is noted on the superior aspect of the septum. Courtesy of: Ashley Davidoff, M.D.
The post mortem specimen reveals the opened left atrium and a view of the anterior leaflet (al) and the posterior leaflet (pl) of the mitral valve. The patent foramen ovale is shown on the septal side of the left atrium. The glistening surface of the endothelium is seen throughout the LA, extending seamlessly onto the mitral valve. It is seen in cross section (white arrow) as part of the the thin smooth and white endocardium, together with a thin myocardial layer (maroon arrow) and pericardial layer (pink arrow). Courtesy of: Ashley Davidoff, M.D.

The heart is distensible, and on occasion in order to examine the heart, the anatomist or pathologist distends the heart in a closed system with fixatives that include formalin, followed by embedding the heart in wax.  The distensibility of the heart enables this process to display a distended heart, as it might appear in vivo.

The post mortem specimen was distended with fixatives including formalin under gravitational pressure, and then fixed in wax. The heart is viewed in a lateral projection, tipped slightly to show the lateral and posterior wall of the LV. The main pulmonary artery (MPA), right ventricular outflow tract (RVOT), left atrial appendage (LAA), aorta (Ao), superior vena cava (SVC), pulmonary vein (PV), left atrium (LA), left ventricle (LV) and inferior vena cava (IVC) are shown. The distensible nature of the heart is demonstrated.
Courtesy of: Ashley Davidoff, M.D.
The reconstructed CT scan is in the same plane as the autopsy specimen above, and shows a distended left ventricle (LV), left atrium (LA) and right atrium (RA). The thin endocardium (white arrows) throughout the heart is one continuous sheet of tissue connected across the whole circulatory system and it is more fibrous in nature. The thin white layer is seen in the left atrium, left atrial appendage (LAA) over the posterior leaflet of the mitral valve (pl) in the left ventricle (LV) and in the right atrium. The surface of the left ventricle, left ventricular outflow tract (LVOT) and right atrium are also lined by the endothelium.All images courtesy: Ashley Davidoff, M.D.

Character: Characterizing the Heart on Imaging

On plain X-ray the the heart is characterized by its soft tissue density which is quite limited except when calcium is present in any of the components, best exemplified by calcific pericarditis.

In the P-A projection the normal heart takes up about 30% of the diaphragmatic surface. Similarly in the lateral projection the heart takes up a third of the diaphragmatic surface. In addition the heart takes up the bottom 1/3 of the retrosternal air space. X-rays characterize tissue by the attenuation characteristics of tissue. This normal chest X-ray defines the heart as soft tissue structure similar in density to the liver and spleen but dissimilar in density to the bone and air and fat. The evaluation is limited for characterization of the heart.
Ashley Davidoff MD

Character: CT Imaging

CT scan is an advanced digital form of X-ray evaluation of the body. Characterization of the tissues is by attenuation of the X-ray as well, except that digital acquisition and cross sectional technique have allowed for significant advance in the characterization of tissue. The density of each structure is reflected and measured by its Hounsfield units.

Character: CT Density Scale in Hounsfield Units

                CT Density Scale in Hounsfield Units
Air -1000        black
Fat -100HU    light black
Water 0HU         dark gray
Soft Tissue about 20-60HU  light gray
Contrast +130       white
Calcification +1000      white
Cancellous bone +400HU  white
CT scanning is the digital form of X-ray evaluation characterizing tissue by revealing their densities. The myocardium is shown as a gray density in image a, and usually measures between 20 and 70 Hounsfield units, being on the low end before contrast and on the high end after contrast. In image b the myocardium is in maroon. The pericardial density is also soft tissue in nature and appears as a thin gray line in (a) and overlaid in white in b. Its CT density is also of a soft tissue nature. It is seen with exquisite detail in this image, despite it being submillimeter in thickness because it is surrounded by fat on either side. The epicardial and pericardial fat are lower density (light gray in a and overlaid in yellow in b). Contrast in the left side of the heart, coronary arteries and pulmonary veins is bright white because this study was timed to optimize the visualization of the coronary arteries. On the other side of the heart, unopacified blood (dark gray) is entering the right atrium at the tail end of the intravenous bolus injection, chasing the last portion of the bolus in the right ventricle which contains a combination of unopacified and opacified blood. A tiny dot of black air is seen in the anterior portion of the RV introduced during the injection. This small amount has no effect on the heart. Ashley Davidoff MD
The CT scan without contrast through the heart, shows a fine, black, curvilinear density in the distal septum and apex, that has a fat density (a,b). This appearance is abnormal and is characteristic of an old apical myocardial infarction. The characterization of the tissue as demonstrated by this CT, is not possible with chest x-ray, and is best seen using CT technology. There is also significant associated thinning of the myocardium also compatible with the prior infarction. There are a few punctate dystrophic calcifications in the septal component of the lucency (a,b). The lucent abnormality also extends to the apex and the free wall of the LV. In images c and d the apex bulges forming an apical aneurysm. The findings are consistent with previous infarction with fatty changes in the infarcted region. Image courtesy of: Ashley Davidoff, MD

Character: Echocardiographic Imaging of Heart Contractibility
The typical method to assess left ventricular function is through the use of M-mode, two-dimensional (2D) imaging and conventional Doppler techniques. The addition of the relatively new techniques of tissue Doppler imaging, strain and strain-rate offers a quantitative method of evaluating systolic ventricular function that is without some of the limitations of traditional methods such as load-dependency and the need for adequate endocardial definition.

This section includes a brief overview of a few echocardiographic methods of assessing contractibility of the heart wall.  For an in depth discussion of these topics, visit the Assessment of LV Systolic Function with TDI, Strain and Strain Rate, Basic Cardiac Color Flow Imaging, Basic Cardiac Doppler, Cardiac Doppler: Normal Flow Patterns, and Echo Assessment of LV Diastolic Function tutorials.

2D and M-mode

2D and M-mode allow for systolic and diastolic linear measurement of ventricular internal dimensions and wall thickness. These measurements allow for LV fractional shortening, ejection fraction and mass calculations. M-mode measurements allow for precise timing of cardiac events. Ejection fraction is after-load dependent. This means that it is affected by the pressure and impedance against which the ventricle must contract.

2D / M-mode Limitations
Causes Results
Oblique orientation Overestimation or underestimation
LV shape alteration Incorrect ejection fraction results
Regional wall motion anomalies
Poor endocardial definition


The modified Simpson’s method or disc summation method allows for calculation of LV volumes from 2D linear and area measurements. These measurements, obtained from the apical 4-chamber and 2-chamber views, provide quantitative evaluation of global LV systolic function with:

adequate systolic and diastolic endocardial definition,
visualization of the entire ventricle without foreshortening,
normal wall motion, and
a normal geometric shape.

To assist in the semi-quantitative 2D evaluation of global systolic function and regional wall motion the LV has been divided into into 3 levels and 16 segments.

This qualitative assessment is through a visual analysis of the function of the ventricle as a whole and of individual wall segments. Transthoracic imaging allows for imaging of all segments; however, accurate assessment requires adequate endocardial definition and complete visualization of the apex without foreshortening.


Conventional Doppler assessment of global LV systolic function includes stroke volume and dP/dt.

Stroke volume is the amount of blood pumped by the heart with each beat. 2D measurement of the left ventricular outflow tract (LVOT) cross-sectional area multiplied by the Doppler velocity time integral of flow through that area, yields stroke volume. A slight error in measuring the LVOT area can cause a significant miscalculation of flow volume. Stroke volume is after-load dependent.

dP/dt (the rate of change in pressure over time) represents the rate of rise of pressure within the ventricle. This measurement requires a clearly delineated mitral regurgitation velocity curve to obtain instantaneous pressure measurements. It is relatively load-independent.

The Doppler Effect
The Doppler effect was first described by the Austrian physicist Christian Johann Doppler in 1842 and refers to a:

“Change in frequency of sound, light, or other waves caused by  the motion of the source or the observer.”

One of the classic examples of this effect is the change in pitch of a train whistle as it moves past a stationary observer.

The train whistle sends out a constant pitch that is perceived by the stationary listener, to increase or decrease upon the speed and direction that the train is traveling.

The stationary train (a) results in no change in pitch. Moving trains pitch changes depending on where the observers stand. The train moving away results in a decrease in wavelength and a decrease in pitch or frequency (b). A train moving towards the observer results in a compression of the wavelength and an increase in pitch. The same phenomenon occurs with light (c).
Image compliments of www.bramboroson.com/…/doppler_overview.jpg


The Doppler Effect

Likewise, as the train moves away from the receiver, the wavelengths are elongated and the frequency of waves, or pitch, is perceived as being decreased.

This change in frequency is a frequency shift.

How does this apply to Doppler imaging of the heart?

The frequency of the reflected ultrasound waves increases when the red blood cells are moving toward the transducer.


The red blood cells are moving toward the transducer, so the frequency of the reflected waves increases.


Conversely, the frequency of reflected ultrasound waves decreases when the red blood cells are moving away from the transducer.


The red blood cells are moving away from the transducer, so the frequency of the reflected sound waves decreases.


In the train example above, a frequency shift is the change in frequency between the transmitted sound and the reflected sound.

In the Heart

In the heart, a frequency shift is induced when a sound wave strikes moving red blood cells.

The velocity and direction of blood flow can be calculated by determining the frequency shifts created.


To determine blood flow direction and velocity, a transducer transmits a known frequency of sound into the heart.

The sound waves reflect off the moving red blood cells, creating frequency shifts. The transducer receives the returning sound.  
The comparison of the transmitted frequency with the returning frequency, determines the frequency shifts created by the moving blood cells.


Moving red blood cells create the frequency shift used to create the spectral tracing in the image above.

Character: Tissue Doppler Imaging

Tissue Doppler Imaging
The previous description applies to general Doppler principles which we generally apply to flow. Tissue Doppler Imaging (TDI) is a technique for the evaluation of global and regional LV systolic function. TDI employs Doppler principles to display the velocity of myocardial motion at any point in the cardiac cycle.

High velocity and low amplitude signals characterize the Doppler signals obtained from fast moving blood flow. However, Doppler signals of relatively dense, slower moving myocardial motion exhibit low velocity and high amplitude signals.

For conventional Doppler, instrument settings maximize the high velocity (>20cm/s), low amplitude blood flow signal. TDI evaluation of myocardial motion requires the suppression of low amplitude signals and the optimization of low velocity (<20cm/s), high amplitude tissue signals. Current ultrasound systems have automatic settings for tissue Doppler interrogation.

Tissue Doppler Techniques: Normal Pulsed Wave 

Pulsed wave TDI allows for the measurement of peak myocardial, ventricular ejection. The myocardial motion of any wall segment can be interrogated with TDI. We know the best angle of incidence is from 0 – 60 degrees.  Due to this angle dependence, the apical views position the myocardium parallel to the transmitted beam.

The mitral annular descent towards the apex represents the left ventricular longitudinal contraction. Decreased global LV systolic function results in diminished mitral annular motion.  Good correlation has been demonstrated between annular velocity and left ventricular ejection fraction over a wide range of ventricular function. Rather than placing the sample volume in the area of flow with TDI, place the sample volume in the myocardium immediately adjacent to the septal or lateral mitral annulus. When imaged in the apical-4 chamber view, this records the longitudinal shortening and lengthening of the mitral annulus. Another location for sample volume placement is the anterior and inferior walls in the apical-two-chamber view.

Pulsed-wave TDI waveform of the lateral wall. Note the Doppler sample volume (arrow) placement in the lateral mitral valve annulus. Image complements of Philips Healthcare, Bothell, WA.

The motion of the ventricular myocardium throughout the cardiac cycle produces three waveforms:

– systolic myocardial velocity reflected above the baseline as the annulus moves toward the apex and towards the transducer.

E – early diastolic myocardial relaxation velocity reflected below the baseline as the annulus moves away from the apex and the transducer.

A – myocardial velocity associated with atrial contraction, reflected below the baseline.
Note: the prime symbol (‘) may used to differentiate tissue Doppler velocities (E’ and A’) from mitral inflow velocities (E and A). Alternatively, lower case “a” for annulus (Ea or Aa) or “m” for myocardial (Em or Am) may be used.

Pulsed wave TDI velocity waveform demonstrating systolic waveforms (S) above the baseline and diastolic waveforms (E and A) below the baseline. Image complements of Philips Healthcare, Bothell, WA.

The normal functioning myocardium contains inherent regional variations.  These changes depend on the sampled level.  Higher TDI pulsed-wave TDI peak velocities occur in the basal segments with much lower velocities obtained from the apical segments. In addition, interrogation of the normal heart at the four basal segments (septal, lateral, anterior and inferior) also demonstrate variation in velocities. PW TDI sampling at the apical level in the apical views demonstrates slight longitudinal motion in the opposite direction of the mid and basal levels.

 PW TDI waveforms taken from six different segments of a normal LV demonstrate normal velocity variance. Image complements of Philips Healthcare, Bothell, WA.


Case Study

Acute infarction is demonstrated by increase water content in the infarcted region characterized by a bright region on T2 weighted sequences.  Myocardial thinning in acute infarction is also present.  However the most specific characterization is manifest by the accumulation of gadolinium in the infarcted region 5-10 minutes after injection.  Delayed enhancement of infarcted myocardium, differentiates normal myocardium from ischemic myocardium.  The area first involved is the subendocardial region, but if the entire wall is involved, transmural delayed enhancement occurs.

Scar tissue is characterized by administering a contrast agent and using a sequence called inversion recovery resulting in black normal myocardium and white scar tissue.

This series of MRI images of the LV and LA are a beautiful sagittal depiction of a normal heart in systole and diastole. Note the changes in LV cavity size as the heart in diastole (a) goes through progressive systole (b,c,d,e,f) and then goes through diastole again. (g,h,i). Courtesy of: Rebecca Schwartz, M.D.
This 34 year old male with sarcoidosis presents with dizziness and complete heart block. The delayed gadolinium study (right image) shows diffuse, non subendocardial enhancement. This is not consistent with ischemia, but rather with cardiomyopathy. Sarcoidosis cardiomyopathy was diagnosed. Courtesy of: Ashley Davidoff, M.D.


The heart is an incredible organ.  Its asymmetric symmetry both in structure and function is a remarkable feat of nature.  The right sided structures are subjected to lower pressures and tend to function as the volume ventricles. Hence structurally they are less muscular, serve the systemic and jugular venous systems to collect blood and provide the lungs with sufficient output to ensure oxygenation of all the cells of the body.  The left sided structures and particularly the left ventricle are built for pressure to ensure that the oxygenated blood gets to all the cells from the head to the toes.  The integration of volume and pressure requirements, are enabled by the delicate second to second, and beat to beat integration of both sides of the heart and both the pulmonary and systemic circulations.

Disease of the heart is very common in Western society, most commonly as a result of coronary artery disease.  The combination of advancing imaging and treatment techniques that have blossomed in the last 20 years has enabled the field to advance understanding and decrease morbidity and mortality .