The myocardium is the thick, muscular middle layer of the heart wall, situated between the outer epicardium and the inner endocardium. It is responsible for the heart's contractile function, enabling it to pump blood throughout the body. The myocardium consists primarily of cardiac muscle tissue, which is unique due to its involuntary nature and ability to contract rhythmically. Proper functioning of the myocardium is essential for maintaining effective circulation and overall cardiovascular health.