The heart is a muscular pump weighing approximately 300 g. It consists of four chambers: the right and left atria and the right and left ventricles (Figure 41.1). The right side of the heart pumps venous blood through the pulmonary circulation for oxygenation, the left heart oxygenated blood through the systemic circulation for distribution to the tissues.

The superior and inferior vena cavae enter the right atrium. There is a small projection, the right auricle, which overlaps the beginning of the ascending aorta. The atrioventricular valves, the mitral and tricuspid valves each consist of a valve ring or annulus, leaflets, anchoring chordae tendinae and papillary muscles. The semilunar valves, the aortic and pulmonary valves comprise three cusps, each with a sinus. The cusps meet at three commissures. The thickness of the wall of the right ventricle is normally 0.25 to 0.3 cm and the left ventricle 0.9 to 1.5 cm.

The heart is surrounded by the pericardial sac, which is composed of two layers of connective tissue (visceral and parietal pericardia) each covered by a layer of mesothelial cells.

The coronary arteries supply blood to the heart (Figure 41.1). The right coronary artery arises from the anterior coronary sinus and runs over the anterior surface of the heart before crossing the posterior surface, where it finally anastomoses with the left coronary artery. Its major branches are the marginal artery and the posterior interventricular artery. There are also atrial and ventricular branches. The left coronary artery arises from the left posterior aortic sinus.

Major branches include the anterior interventricular artery and the circumflex artery. The anterior interventricular artery descends towards the apex and anastomoses with the posterior interventricular artery. A diagonal branch runs to the left ventricle. The circumflex artery anastomoses with the terminal branch of the right coronary artery. It gives off the marginal artery, which runs along the left border of the heart.

The heart is composed of three layers, the epicardium (serous pericardium), the muscular myocardium and the endocardium.

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