Science, Tech, Math › Science Myocardium of the Heart Share Flipboard Email Print Science Biology Anatomy Basics Cell Biology Genetics Organisms Physiology Botany Ecology Chemistry Physics Geology Astronomy Weather & Climate By Regina Bailey Biology Expert B.A., Biology, Emory University A.S., Nursing, Chattahoochee Technical College Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in "Kaplan AP Biology" and "The Internet for Cellular and Molecular Biologists." our editorial process Regina Bailey Updated January 13, 2020 Myocardium Definition Falty14 /Wikimedia Commons/CC by SA 4.0 Myocardium is the muscular middle layer of the wall of the heart. It is composed of spontaneously contracting cardiac muscle fibers which allow the heart to contract. Heart contraction is an autonomic (involuntary) function of the peripheral nervous system. The myocardium is surrounded by the epicardium (outer layer of the wall of the heart) and the endocardium (inner layer of the heart). Function of the Myocardium Myocardium stimulates heart contractions to pump blood from the ventricles and relaxes the heart to allow the atria to receive blood. These contractions produce what is known as a heart beat. The beating of the heart drives the cardiac cycle which pumps blood to cells and tissues of the body.