Which phase of the cardiac cycle is associated with repolarization?

Repolarization in the cardiac cycle primarily occurs during Phase 3. This phase is characterized by the return of the cardiac muscle cells to their resting state after depolarization. During Phase 3, there is a closure of sodium channels and an increase in potassium permeability, allowing potassium ions to flow out of the cell. This efflux of potassium restores the negative membrane potential, resulting in repolarization of the cell.

This is crucial for re-establishing the resting state of the cardiomyocytes, ensuring that they are ready for the next cycle of excitation and contraction. This process is essential for maintaining the rhythm of the heart and ensuring that it can contract effectively in response to electrical signals.

In contrast, the other phases mentioned are not primarily associated with repolarization. Phase 1 involves initial repolarization and a brief outward potassium current, but it does not complete the process. Phases 2 and 5 are also associated with other aspects of electrical conduction and contraction in the cardiac muscle. Therefore, identifying Phase 3 as the correct answer highlights the significance of the complete repolarization process within the cardiac cycle.