The heart is a muscular organ specialised to pump and circulate blood throughout the body constantly. The wall of the heart is made up of three layers i.e., myocardium (middle layer), endocardium (inner layer), and epicardium (outer layer).

The muscles that are found in the wall of the heart are strong, cylindrical, and branched. They are known as cardiac muscles. The cardiac muscles contract rhythmically and are not controlled voluntarily. These muscles have striations and their cells (cardiomyocytes) contain only one nucleus. These are the only muscles in the body that do not get tired.