CVS Practice Test 2025 - Free CVS Practice Questions and Study Guide

The primary phase during which potassium efflux occurs is Phase 3 of the cardiac action potential. During this phase, the repolarization of the cardiac myocytes takes place, which is largely due to the efflux of potassium ions from the cells.

As the action potential progresses, the influx of sodium and calcium during the earlier phases creates a depolarized state, but in Phase 3, voltage-gated potassium channels open, allowing potassium to flow out of the cell. This outflow of potassium ions is essential for restoring the negative membrane potential, leading to repolarization.

This repolarization process is crucial for setting the stage for the next heartbeat and ensuring that the cardiac cycle progresses smoothly. It plays a significant role in regulating heart rhythms, and any disruption in this phase can lead to arrhythmias.

Phases 0, 1, and 4 have different ion activities where sodium primarily enters during Phase 0, transient outward potassium currents occur in Phase 1, and Phase 4 usually represents a resting state with leakage of potassium but not the significant efflux seen in Phase 3.