What is the myocardium?

• A. The thick, muscular middle layer of the heart, composed of cardiac muscle.
• B. The thin outer layer of the cardiac wall.
• C. The inner lining of the heart chambers.
• D. The fibrous outer covering surrounding the heart.

Answer: (A)

The myocardium is the thick, muscular middle layer of the heart wall that contracts to pump blood. It’s made of cardiac muscle cells (cardiomyocytes) arranged to produce strong, coordinated contractions, with intercalated discs and gap junctions that help electrical signals spread quickly for a synchronized heartbeat. The myocardium lies between the inner lining, called the endocardium, and the outer layer, the epicardium (the visceral layer of the pericardium). Its blood supply comes from the coronary arteries, so blockage here can lead to myocardial infarction and tissue damage. The other terms describe surrounding structures: the thin outer layer of the heart wall is the epicardium, the inner lining of the chambers is the endocardium, and the fibrous outer covering is the fibrous pericardium.