Cardiovascular System – Heart Anatomy, Function, and Circulatory Pathways Practice Test

Endocardium is the innermost layer of the heart wall, lining the chambers and covering the valve surfaces. It’s a thin, smooth layer of endothelial cells (with a subendocardial connective tissue layer) that creates a friction-reducing surface for blood flow and provides a barrier between the blood and the muscular heart tissue. This inner lining is distinct from the thicker muscular middle layer, which is the myocardium and does the pumping, and from the outer layers: the epicardium (visceral pericardium) that covers the heart’s exterior, and the fibrous pericardium forming the tough outer sac.