The heart wall has three layers with different functions; an outer layer for protection, a middle muscle layer that contracts and an inner layer that provides a smooth surface for collecting blood.
The Epicardium (epi = outside) is a thin layer of connective tissue and fat. It helps to protect and lubricate the external surface of the heart.
The Myocardium (myo = muscle) is the middle muscular layer made up of thick cardiac muscles. This forms the major structure and thickness of the heart. These muscles are responsible for the “pumping action” and their thickness allows them to pump blood vigorously under high pressure without bursting.
The Endocardium (endo = inside) is made up of a transparent thin smooth layer of cells that line the inside of the heart. They provide a smooth lining for the valves and chambers of the heart and also facilitate smooth, consistent flow of blood, preventing blood clots from forming inside the heart. These smooth linings extend from the heart and are continuous with the large blood vessels attached to the heart.