myocardium

The myocardium is the thick middle muscular layer of the heart wall, located between the endocardium and the epicardium. It is composed primarily of cardiomyocytes, specialized striated muscle cells arranged in a network that enables forceful, coordinated contraction. The myocardium forms the walls of the ventricles most prominently, with the left ventricle having a thicker wall to generate higher pressure for systemic circulation.

Cardiomyocytes are connected at intercalated discs, which contain desmosomes, adherens junctions, and gap junctions that permit rapid electrical coupling and synchronized contraction. Contraction is controlled by the cardiac conduction system, comprising the sinoatrial node, atrioventricular node, and the His-Purkinje network, and is modulated by autonomic nerves and circulating hormones.

Blood supply to the myocardium is provided by the coronary arteries; ventricular perfusion occurs mainly during diastole. The tissue has high oxidative capacity, with abundant mitochondria, and relies primarily on fatty acids for energy, using glucose and lactate as supplementary substrates.

Pathologies affecting the myocardium include ischemia and infarction, myocarditis, and various cardiomyopathies. Repair after injury can lead to fibrosis and remodeling, contributing to heart failure. Biomarkers such as troponins aid in diagnosing myocardial injury. Developmentally, the myocardium originates from mesodermal tissue of the heart tube, and mature myocardium exhibits limited regenerative capacity.