Myocardium

The myocardium is the muscular middle layer of the heart wall composed primarily of specialized cardiac muscle cells called cardiomyocytes that contract to pump blood throughout the body. 

The myocardium is covered by the visceral layer of the serous pericardium (epicardium), and lined by the endocardium).

The myocardium is composed of cardiomyocytes arranged in a highly organized, three-dimensional meshwork.These cardiomyocytes are supported by a collagenous fibrous matrix with epimysial, perimysial, and endomysial components, which provide structural integrity and facilitate force transmission during contraction.