Which type of muscle tissue is involuntary and found in the heart?

Cardiac muscle is the correct answer because it is the type of muscle tissue that is specifically found in the heart. This muscle tissue is involuntary, which means it operates automatically without conscious control, allowing the heart to continuously pump blood throughout the body.

Cardiac muscle has a unique structure characterized by striations and a branching pattern, which distinguishes it from skeletal muscle that is also striated but under voluntary control. Smooth muscle, on the other hand, is involuntary and found in various organs but not in the heart itself. Striated muscle can refer generically to both skeletal and cardiac muscle, but within the context of the heart, "cardiac muscle" is the precise term that identifies the specific muscle type responsible for heart function.