The muscle responsible for the contraction of the heart is the myocardium. This specialized muscle tissue composes the heart's middle layer and is essential for pumping blood throughout the body. Unlike skeletal muscles, which are under voluntary control, the myocardium operates involuntarily, meaning its contractions are regulated by the heart's electrical conduction system without conscious effort. The rhythmic contractions of the myocardium allow the heart to efficiently fill with blood and then pump it out into the circulatory system, sustaining life by providing oxygen and nutrients to various organs and tissues.