What is the role of the myocardium?

• A. To contract and pump blood throughout the body.
• B. To serve as the inner lining of the heart chambers.
• C. To protect the heart with a fibrous layer.
• D. To regulate heart rate via electrical impulses.

Answer: (A)

The myocardium is the heart’s muscular layer that contracts to pump blood. When the myocardium shortens during systole, it squeezes the heart chambers and forces blood out into the aorta and pulmonary artery, generating the force needed to circulate blood to the lungs and to the rest of the body. The strength and coordination of this muscular layer determine cardiac output, and the left ventricle tends to have the thickest myocardium because it must generate higher pressure to deliver blood systemically.

The other options describe different cardiac structures: the inner lining of the heart chambers is the endocardium; the fibrous layer that protects the heart is the pericardium; and regulating heart rate via electrical impulses is the job of the conduction system (nodes and pathways) that coordinates, rather than constitutes, the myocardium itself.