Anatomy of the heart external and internal features of the heart

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Assistant Editor(s)-in-Chief: Rim Halaby, Yazan Daaboul

• The heart wall consists of 3 layers:
  • Epicardium: thin external layer formed by visceral layer of serous pericardium
  • Myocardium: thick middle layer made of cardiac muscle
  • Endocardium: thin internal membrane that lines the heart and its valves. It is composed of endothelium and sub-endothelial connective tissue, similar to intimal component of blood vessels.

• The heart and roots of great vessels are embedded in the pericardial sac, approximately in the center of the thorax. The size of the heart is slightly larger than a clenched fist. The heart is surrounded laterally and posteriorly by the lungs, and anteriorly bound by the sternum and medial sections of the ribs and sterno-costal joints.
• It has the shape of a three-sided pyramid with an apex (left anterior), a base (posterior), and 4 surfaces: Sterno-costal/anterior (formed by right ventricle), diaphragmatic/inferior (formed by left ventricle and part of right ventricle), left pulmonary (formed by left ventricle, in contact with left lung), and right pulmonary (formed by right atrium).
• The heart appears trapezoid in the posterior and anterior views. As such, it consists of 4 borders: Right (convex), Inferior (horizontal), left (oblique), and superior.

Below is an image showing a schematic outline of the heart in the mediastinum.

• The external surface of the heart is notable for 3 main sulci (grooves):
  • Coronary (atrioventricular) sulcus: runs around the heart, and separates atria from ventricles
  • Anterior interventricular sulcus: runs along the interventricular septum anteriorly
  • Posterior interventricular sulcus: runs along the interventricular septum posteriorly

• The heart has 4 chambers: Right and left atria and right and left ventricles.
• Blood flows normally in the right to left direction: Right atrium to right ventricle to left atrium, and finally to left ventricle.
• Oxygen-depleted blood reaches the right atrium via the coronary sinus and superior and inferior vena cava and evacuates the right ventricle via the pulmonary artery towards the lungs.
• Oxygen enriched blood then re-enters the left atrium via 4 pulmonary veins and evacuates the left ventricle via the aorta.

Below is an image showing the atria and ventricles of the heart as well as arrows indicating the normal blood flow throught the heart valves.

• 
  Anterior (frontal) view of the opened heart. White arrows indicate normal blood flow.

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