Cardiac muscles are part of the three types of muscles in the body. The other two are the smooth and the skeletal muscles. It makes up the muscular layer of the heart. Each time the heart contracts, the individual muscle cells shorten and thus, cause the continuous beating. In order to understand the functions better, take a look at it under the microscope.
The individual cardiac muscle has a cylindrical shape, almost similar with the skeletal muscle. It also has an alternating light and dark band representing the proteins, actin and myosin. However, unlike the skeletal muscles, the cardiac fibers branch out. Intercalated discs are the most prominent features of the cardiac muscle. These are junctions that increase the point of communication among the cells. It has one or two centrally located nuclei. If you use an electron microscope, you will see the presence of the thin and thick filaments. The combination of these myofilaments makes up the sarcomere, which is the contractile unit of the muscle.
The cardiac muscle is involuntarily controlled. The nervous system controls the number of times the heart will beat in a minute. That makes it sensible to say that even when you are asleep, your heart continues to pump blood to all parts of your body. Aside from the control of the central nervous system, the presence of autorhythmic fibers keeps the heart beating. The depolarization of these fibers causes the cardiac muscle to beat for a number of times per minute. The pacemaker of the heart is the sino-atrial node, which transmits the action potential to the atrioventricular node, which then branches out to the purkinje fibers.
Because of the forceful activity of the left ventricles, you expect a more muscular layer in this site compared to the right ventricle. By knowing the histology of the heart, you can better appreciate the works of your cardiac muscle.