Layers of the Heart Wall

The heart wall has three layers—the epicardium, the myocardium, and the endocardium.

The outermost layer, the epicardium, is the visceral layer of the serous pericardium. Its outer surface is made of thin and transparent mesothelium, while the inner layer is made of areolar connective tissue with large fat deposits that increase with age.

The middle layer, the myocardium, is the thickest. It comprises interconnected cardiac muscle cells held together by crisscrossing connective tissue fibers. These muscular bundles contract, generating the pumping motion of the heart.

The innermost layer, the endocardium, is a thin endothelial lining on top of a layer of connective tissue. It lines the inner surfaces of the heart and provides a smooth surface for its chambers and valves, reducing friction as the blood flows.

The heart wall contains four connective tissue rings that encircle the valves and fuse with the interventricular septum.

This dense connective tissue network, known as the fibrous or cardiac skeleton, gives structural support and prevents overstretching of the valves.