What is the name of the muscle that makes up the heart?

The muscle that makes up the heart is called the myocardium. This term specifically refers to the middle layer of the heart wall, which is composed of cardiac muscle tissue. The myocardium is responsible for the contracting action that pumps blood throughout the body, making it essential for the heart's function.

Cardiac muscle, while closely related, is a broader category that refers to the type of muscle tissue found in the heart but does not specify the layer. Skeletal muscle, on the other hand, is under voluntary control and makes up the muscles responsible for body movements, which is distinct from the involuntary nature of the heart muscle. Visceral muscle generally refers to smooth muscle found in internal organs, which is different from both cardiac and skeletal muscle. Thus, referring to the muscle that specifically constitutes the heart wall, myocardium is the correct term.