Involuntary muscles are muscles that are not controllable consciously, and instead contract due to unconscious impulses sent by the autonomic nervous system or certain specialized cells or hormones.Both smooth muscle and cardiac muscle can be classified as involuntary muscles.Smooth muscle is comprised of spindle-shaped cells that have no striations and is found in numerous locations throughout the human body. Cardiac muscle is striated rather than smooth, and is found only within the walls of the heart. beating heart is one of the best examples of an involuntary muscle. Contractions of cardiac muscles push blood through the four chambers of the human heart. The process of peristalsis, which pushes food through the esophagus and small intestine, is controlled by involuntary muscles.