Subscribe to our newsletter. Ask an Expert The Heart and the Circulatory System Heart Anatomy From this point forward, all discussions about the heart and circulation refer to human circulation. The human heart is a muscular pump. While most of the hollow organs of the body do have muscular layers, the heart is almost entirely muscle. Unlike most of the other hollow organs, whose muscle layers are composed of smooth muscle, the heart is composed of cardiac muscle.
All muscle types function by contraction, which causes the muscle cells to shorten.
Skeletal muscle cells, which make up most of the mass of the body, are voluntary and contract when the brain sends signals telling them to react. The smooth muscle surrounding the other hollow organs is involuntary, meaning it does not need to be told to contract. So functionally, cardiac muscle and smooth muscle are similar. Anatomically though, cardiac muscle more closely resembles skeletal muscle. Both skeletal muscle and cardiac muscle are striated.