Which layer of the heart is known as the muscular layer?

The muscular layer of the heart is the myocardium. This layer is primarily composed of cardiac muscle tissue, which is responsible for the contractile function of the heart. The myocardium facilitates the pumping action that allows blood to be efficiently circulated throughout the body. Its unique structure and properties enable it to generate the force necessary for heart contractions and to withstand the continuous stress of each heartbeat.

In contrast, the epicardium, which is the outer layer of the heart wall, serves as a protective layer and is part of the pericardial sac that encases the heart. The endocardium is the thin inner lining of the heart chambers and valves, providing a smooth surface to minimize friction during blood flow. The pericardium, a double-walled sac, surrounds the heart and serves primarily to protect it and prevent overexpansion. Each of these layers has a distinct role, but it is the myocardium that is specifically identified as the muscular layer crucial for the heart's pumping function.