Which part of the heart is described as muscular?

The myocardium is the thick, muscular layer of the heart wall. It is responsible for the heart's ability to contract and pump blood throughout the body. This muscular layer is essential for the heart's function, as it provides the strength and capability needed for the cardiac muscle to perform its vital role in maintaining circulation.

The endocardium, while it plays a crucial role in lining the interior of the heart chambers and valves, is not muscular; it is more of a smooth membrane that prevents blood from clotting and provides a smooth surface for blood flow. The pericardium is a double-layered sac that surrounds the heart, providing protection and anchoring it within the chest, but it is not muscular either. The epicardium is the outer layer of the heart, also not muscular, serving as a protective layer alongside the pericardium.

Understanding the unique functions and structures of each layer helps clarify why the myocardium is specifically identified as the muscular component of the heart.