During which phase does ventricular contraction occur in the cardiac cycle?

Ventricular contraction occurs during Phase 2, also known as the plateau phase of the cardiac cycle. During this phase, the cardiac muscle cells experience a prolonged depolarization. This is primarily due to the influx of calcium ions through voltage-gated calcium channels, which helps sustain the contraction of the ventricles. As a result, the ventricles are actively contracting, pumping blood into the aorta and pulmonary artery, which is crucial for circulating blood throughout the body.

Understanding the sequence of the cardiac cycle is essential, as it highlights the complex interactions of electrical and mechanical activities of the heart. Phase 2 follows the rapid depolarization of Phase 0, where sodium ions predominantly enter the cells and create the initial spike in action potential, and it precedes the repolarization that occurs in Phase 3, where potassium ions exit the cells and bring the membrane potential back to its resting state. This balance of ion movements and the resultant contraction phases are vital for effective heart function and maintaining hemodynamics in the body.