What are the layers of the heart wall?

• A. Epicardium, pericardium, and endocardium.
• B. Epicardium, myocardium, and endocardium.
• C. Pericardium, epicardium, and myocardium.
• D. Endocardium, myocardium, and pericardium.

Answer: (B)

The heart wall is built from three layers: the epicardium on the outside, the myocardium in the middle, and the endocardium lining the chambers on the inside. The epicardium is the outermost layer and, in fact, is the visceral layer of the pericardium, providing a protective surface and containing vessels that supply the heart. The thick middle layer, the myocardium, is made of cardiac muscle and is responsible for the heart’s pumping action. The inner layer, the endocardium, lines the chambers and covers the heart valves, continuing with the endothelium of the great vessels.

The pericardium surrounds the heart as a fibrous sac, with a parietal layer lining the outer area and a potential space called the pericardial cavity. It is not considered part of the heart wall itself, which is why options that include the pericardium as a wall layer aren’t correct.