The epicardium of the heart muscle

The epicardium is the outermost layer of the heart wall and is composed of a thin layer of connective tissue covered by mesothelial cells. Histologically, the epicardium appears as a single layer of flat, squamous cells on the surface of the heart. Lymphocytes should not normally be present in the heart as seen in this image. Notice the cross section of the nerve exposing a magnitude of nerve fiberes within. The cardiomyocytes are cut across in this image contrary to a longitudinal section.

The epicardium plays several important roles in the function of the heart. One of its primary functions is to provide a smooth, lubricated surface that allows the heart to contract and relax without friction. The mesothelial cells that cover the epicardium secrete a fluid called pericardial fluid, which lubricates the surface of the heart and reduces friction between the heart and surrounding structures.