During which phase of the cardiac cycle does diastole occur?

Diastole is the phase of the cardiac cycle when the heart chambers relax and fill with blood. This phase is crucial for maintaining adequate blood flow throughout the body. During diastole, the heart muscle is not contracting; instead, it is in a relaxed state which allows the atria and ventricles to accommodate incoming blood.

While blood does fill the atria during this phase, the heart itself is relaxing, which is a key distinction that highlights why relaxation is the defining feature of diastole. Additionally, electrical activity occurs throughout the cardiac cycle but does not specifically define the diastolic phase, as it is associated with both contraction and relaxation periods. Understanding that diastole is primarily characterized by the relaxation of the heart chambers clarifies its role in the overall functioning of the cardiovascular system.