Which layer of the heart is primarily responsible for contraction?

The myocardium is the thick, muscular layer of the heart and is primarily responsible for contraction. This layer contains the cardiac muscle fibers that enable the heart to pump blood effectively throughout the body. When the myocardium contracts, it generates the force necessary to push blood out of the heart during systole (the contraction phase) and is crucial for maintaining circulation.

In contrast, the endocardium is the thin inner lining of the heart chambers, mainly serving a protective function; the epicardium is the outer layer that covers the heart and contains blood vessels and connective tissue; and the pericardium is a double-walled sac that surrounds the heart, providing it with protection and anchoring it within the thoracic cavity. Though all these layers are important for heart structure and function, the propagation of blood through contraction is solely the role of the myocardium.