Endocardium is a thin layer of connective tissue with smooth muscle cells.

Myocardium is the thickest layer and consist mainly of cardiac muscle with its fibers arranged spirally around each heart chamber.

Epicardium is the visceral layer of the pericardium and is covered by the simple squamous-to-cuboidal epithelium that also lines the pericardial space. It is the site of the coronary vessels and contains considerable adipose tissue.