What is one characteristic of cardiac muscle contraction?

Cardiac muscle contraction is characterized by being involuntary, meaning it is not under conscious control. This involuntary nature allows the heart to continue beating autonomously without requiring deliberate effort from the brain. The heart's pacemaker cells automatically trigger contractions, regulating the heartbeat rhythm continuously to meet the body’s demands for blood and oxygen, regardless of physical activity levels or the individual's awareness.

The other options suggest qualities that do not apply to cardiac muscle. For example, suggesting that it is under conscious control or voluntary implies that one could choose when to move their heart muscle, which is not the case. The heart operates continuously and autonomously, responding to the body's needs rather than to voluntary signals. The idea that cardiac contractions occur only during exercise is also incorrect, as the heart beats continuously whether at rest or during activity to maintain essential bodily functions.