What is the term for the thick muscular portion of the heart?

The term for the thick muscular portion of the heart is myocardium. The myocardium is the middle layer of the heart wall and is composed of cardiac muscle tissue. This layer is crucial for the heart's ability to pump blood effectively, as the myocardial contraction generates the force necessary to propel blood into the circulation. The thickness of the myocardium varies in different chambers of the heart, being particularly robust in the ventricles, which handle the high pressure required to circulate blood throughout the body.

Focusing on the other terms, the epicardium refers to the outer layer of the heart wall, which also serves as a protective layer. The endocardium is the innermost layer that lines the chambers and valves of the heart, providing a smooth surface for blood flow. The pericardium is a double-walled sac that encases the heart and contains fluid, allowing for lubrication and protection against surrounding structures. Understanding these layers and their functions emphasizes why the myocardium is recognized specifically as the muscular component essential for cardiac function.