The muscle layer of the heart is the:

• A. Pericardium
• B. Epicardium
• C. Myocardium
• D. Endocardium

Answer: (C)

The muscle layer of the heart is the myocardium. The heart wall has three layers: the outer epicardium, the middle myocardium, and the inner endocardium. The epicardium is a thin protective surface, part of the outer covering. The endocardium lines the chambers and covers the valves. The myocardium, in the middle, is made of cardiac muscle tissue that contracts to pump blood; it contains cells connected by intercalated discs to coordinate a strong, synchronized heartbeat. The muscular layer is thickest in the left ventricle because it must generate the force to propel blood through the systemic circulation.