Epicardium

The epicardium is the outermost layer of the heart and corresponds to the visceral layer of the serous pericardium that covers the heart (serous pericardium also covers the great mediastinal vessels but this part is not included in the term "epicardium")

The epicardium is tightly adherent to the myocardium and separated from the parietal pericardium by the pericardial cavity containing a small amount of serous fluid.

The epicardium is composed of a single layer of mesothelial cells that directly overlies a thin layer of connective tissue, which may contain variable amounts of epicardial adipose tissue. This adipose tissue is most prominent along the atrioventricular and interventricular grooves and over the right ventricle, and it houses the major coronary arteries, cardiac veins, lymphatics, and nerves.