During which phase does the heart contract?

The heart contracts during the systole phase, which is a critical part of the cardiac cycle. During systole, the ventricles of the heart contract, pumping blood out of the heart to the lungs and the rest of the body. This contraction is essential for maintaining blood circulation and ensuring that oxygenated blood reaches the tissues while deoxygenated blood is sent to the lungs for reoxygenation.

In contrast, diastole refers to the phase when the heart muscle relaxes and the chambers fill with blood. The cardiac cycle encompasses both systole and diastole, representing the complete cycle of heart activity, but it does not specifically identify the contraction phase. An electrocardiogram is a diagnostic tool used to visualize the electrical activity of the heart but does not refer to a phase of the heart's action. Therefore, the correct identification of the contraction phase of the heart as systole highlights its vital role in effective cardiovascular function.