What is the main characteristic of the epicardium layer of the heart?

The epicardium is indeed the outermost layer of the heart wall, which serves as a protective layer for the heart. Composed of a thin layer of connective tissue and epithelium, it also contains blood vessels, nerves, and fat, providing support and protection to the heart structures beneath it. This layer plays a crucial role as it directly interfaces with the surrounding structures in the thoracic cavity.

In the context of the heart wall, the other layers—including the myocardium, which is the thickest layer responsible for the contractile function of the heart, and the endocardium, which lines the chambers and valves—serve different purposes. The presence of pacemaker cells is specific to the sinoatrial node and other areas of the myocardium, not the epicardium. Additionally, the main function associated with oxygen exchange happens primarily in the myocardium, where the blood supply and oxygenation occur, rather than in the epicardium. Thus, recognizing the epicardium as the outermost layer is essential for understanding the structural organization of the heart.