Anatomy of the Heart

The pictures below are from dissections of fresh pig hearts.  Hopefully these will allow you to appreciate the nature of the tissues in the heart much more effectively than you ever could by just looking at a model. 

Recommended Reading

Read pages 440-446 in Silverthorn, focussing on figure 14.5.

External Features of the Heart

The heart is contained within a thin membranous sac, the pericardium. The small picture at right shows a bit of the cut pericardium on the posterior surface of the heart.  Optional:  To get a sense of the relationship of the heart and the pericardium in the body, you can look at Video 5.1.9 from Acland's Video Atlas of Anatomy (the link opens in a new tab).

The picture below shows an anterior view of the heart with the pericardium removed.  The letters indicated in the text refer to the labels on the picture.

The anterior surface of the heart is characterized by the presence of the large arteries leaving the base of the heart, the pulmonary trunk (H) and the aorta (G).  The pulmonary trunk is the vessel that divides to give rise to the two pulmonary arteries going to each lung.  The pulmonary trunk is somewhat anterior to the aorta, and although it is connected to the right ventricle, it tilts leftward.  The aorta is slightly posterior to the pulmonary trunk and bound to it by connective tissue.  Note that when you look at the anterior surface of the heart (or at anatomical illustrations of the heart in books or on the internet) the right side of the heart will be on your left, and the left side of the heart will be on your right.

The inferior part of the heart is called the apex (A) because it comes to a point, like the apex of a cone. The superior part of the heart is referred to as the base (B). The major vessels of the heart are found at the base of the heart, along with the upper chambers, the right atrium (C) and left atrium (D). The atria are collapsed, but in a functioning heart, they would be stretched full of blood. 

The majority of the heart tissue consists of the ventricles.  The left ventricle (F) is stiff and solid because it is very thick-walled.  By contrast, the right ventricle (E) has thinner walls, and would collapse a little if you poked it.

Internal Features of the Heart

The figure at right shows a sectioned heart where you can see the internal structures of the heart.  The left and right ventricles are separated by the large interventricular septum (A).  Note the relative thickness of the walls of the right ventricle (B) and left ventricle (C). The inner surface of the heart is covered with irregular bands of tissue known as trabeculae carneae.  The papillary muscles (D; red arrows) are distinct little hills of muscle that poke up from the inner surface of the heart.  At the tips of the papillary muscles are the chordae tendineae (E; yellow arrows), strings of connective tissue that attach to the edges of the atrioventricular valves (AV valves).

The heart contains four important valves that ensure that blood flows in one direction.  The right AV valve (tricuspid valve) and the left AV valve (mitral valve) lie between the atria and ventricles, and prevent blood from flowing back into the atria when the ventricles contract (systole).  The pulmonary valve and the aortic valve lie at the beginning of the large outflow vessels at the base of the heart, and prevent blood from falling back into the heart when the ventricles are relaxed (diastole).

The valves consist of two or three cusps (also called leaflets) of delicate connective tissue that come together to block the flow of blood.  The valves in the vessels (called the semilunar valves) each have three valve cusps that look like little pockets or like half-moons (hence the name "semilunar").  The valve cusps of the AV valves look like torn curtains, and are easily identified because they have the chordae tendineae attached to them.  All four heart valves are located at the same plane in the heart and are attached to a fibrous layer of connective tissue called the cardiac skeleton. This is shown in the illustration of the transverse section of the heart, Figure 14.7b on p. 444.  The image at right shows the same heart as the one above, with a pin through one of the cusps of the pulmonary valve and the left AV valve labeled "L-AV".

The image below shows a different heart that is dissected to show the aortic valve.  An unlabeled photo on the left allows you to fully see the structures.  PV:  pulmonary valve.  PM:  papillary muscle.  L-AV:  left AV valve (mitral valve).  S:  interventricular septum.  Although not labeled, on these figures you should also be able to identify the chordae tendineae and the left atrium.

Video 5.1.6 ("Ventricles: outflow pathways") is particularly useful for showing the structure and action of the valves. The action of the valves is shown by pumping water through the heart. When they are open, the valve cusps fall back against the tissue walls. When the valves close, the edges of the cusps come together. When viewed from the top, the three cusps of a closed semilunar valve look like the Mercedes Benz logo.