The muscle responsible for the heartbeat is the myocardium. This specialized muscle tissue makes up the walls of the heart and is crucial for pumping blood throughout the body. The myocardium contracts rhythmically and involuntarily, allowing the heart to perform its vital function of circulating oxygen-rich blood to tissues and organs while returning deoxygenated blood to the lungs. The contraction of the myocardium is controlled by electrical impulses generated in the sinoatrial (SA) node, which regulates the heart rate. Proper function of the myocardium is essential for maintaining overall cardiovascular health and supporting bodily functions.