What serves as the structural framework for the heart?

The myocardium serves as the structural framework for the heart because it is the thick, muscular middle layer of the heart wall responsible for the contraction and pumping action of the heart. This layer is composed predominantly of cardiac muscle tissue, which allows it to generate the force necessary to pump blood throughout the body. The myocardium is crucial for maintaining the heart's shape and function, providing the strength and elasticity needed for effective cardiac cycle performance.

In contrast, the endocardium is a thin innermost layer lining the heart chambers, mainly serving a protective function and facilitating smooth blood flow, but it does not provide structural support. The epicardium, while it is the outermost layer of the heart and provides a protective covering, does not contribute to the heart's structural integrity in the same way that the myocardium does. The pericardium, on the other hand, is a fibrous sac surrounding the heart that protects it and prevents overexpansion, but it is not part of the heart's actual structure.