Which term refers to the muscle that surrounds the heart?

The correct term for the muscle that surrounds the heart is cardiac muscle. This type of muscle is specifically designed to support the unique function of the heart, allowing it to contract rhythmically and continuously throughout an animal's life without fatigue. Cardiac muscle cells are striated like skeletal muscle but differ in that they are interconnected by intercalated discs, which facilitate the synchronization of heart contractions. This ensures that the heart beats as a coordinated unit, which is essential for effective blood circulation.

Skeletal muscle, while also striated, is under voluntary control and is primarily responsible for movement of the skeletal system, not the heart. Visceral muscle is a term often used to describe smooth muscle found in internal organs, which is not involved in the contractions of the heart. Smooth muscle, another type of involuntary muscle, is found in hollow organs and blood vessels but does not have the striated appearance of cardiac muscle and does not have the specialized function of pumping blood. Thus, the characteristics and specific functions of cardiac muscle make it the correct answer regarding the muscle surrounding the heart.