What refers to the period in which the mechanical and electrical events of the heart are relaxed and involves repolarization?

The correct answer is diastole, which refers to the phase of the cardiac cycle when the heart muscles relax. During diastole, the chambers of the heart fill with blood in preparation for the next heartbeat. This relaxation phase is critical as it allows for the repolarization of cardiac muscle cells, restoring their electrical potential after the preceding contraction (systole) has occurred. The electrical events associated with repolarization occur as potassium ions move out of the cells, leading to a return to the resting membrane potential, enabling the heart to be ready for the next electrical impulse.

Understanding diastole is vital because it emphasizes the heart's rhythm and function during rest. In contrast, when the heart is in systole, it is actively contracting and pumping blood, which involves different electrical and mechanical events. Arrhythmia refers to irregular heartbeats and is not a phase of the cardiac cycle, while contractility describes the strength of the heart's contraction but does not pertain to the relaxation phase specifically. This distinction highlights the importance of diastole in maintaining a well-functioning cardiovascular system.