What is the specific function of the cardiac muscle?

Cardiac muscles are involuntary and keep the heart pumping. Cardiac muscles have specialized cells known as pacemaker cells that control the contractions of the heart. 

The cardiac muscle is responsible for the heart's contractility and, consequently, its pumping motion. The heart must contract with sufficient force and blood to meet the metabolic needs of the entire body. The definition of cardiac output is heart rate multiplied by stroke volume.

There are just cardiac muscles in the heart. They govern the contraction and relaxation of the heart, thus aiding in the circulation of blood. The contractions of the heart are involuntary. They are essential for maintaining life.

In vertebrates, cardiac muscle, commonly known as myocardium, is one of three primary muscle groups found exclusively in the heart. In possessing contractile units known as sarcomeres, cardiac muscle is comparable to skeletal muscle, another main muscle type but distinct from smooth muscle, the third major muscle type.

In contrast to skeletal muscle, cardiac muscle shows regular contractions and is not subject to voluntary control. The sinoatrial node of the heart regulates the rhythmic contraction of cardiac muscle, serving as the heart's pacemaker.