Which heart layer lines the heart chambers and valves?

• A. Endocardium
• B. Epicardium
• C. Myocardium
• D. Pericardium

Answer: (A)

The inner lining of the heart chambers and valves is the endocardium. It is a thin, smooth layer of endothelial tissue that covers the interior surfaces, including the heart valves, providing a low-friction surface for blood flow and protecting the heart muscle beneath. This distinguishes it from the other layers: the myocardium is the thick muscular layer that contracts to pump blood; the epicardium is the outer surface of the heart, and the pericardium is the fibrous sac that surrounds the heart. The endocardium’s smooth lining helps blood move efficiently and also relates to parts of the conduction system located just beneath its surface.