What occurs during Phase 3 of the cardiac cycle?

During Phase 3 of the cardiac cycle, repolarization occurs. This is a crucial phase that follows depolarization, which happens in Phase 0 and is characterized by the rapid influx of sodium ions causing the interior of the cardiac cells to become positively charged.

In Phase 3, the cardiac myocytes begin to return to their resting state. This is achieved through the efflux of potassium ions from the cells, leading to a decrease in the positive charge inside the myocytes and a return to a negative resting potential. Repolarization is essential for resetting the electrical state of the cardiac cells so they can prepare for the next cycle of depolarization and contraction.

This phase ensures that the heart muscle can relax and refill with blood before the next contraction, promoting a coordinated cardiac cycle and maintaining effective blood circulation. Understanding the significance of repolarization during this phase helps to grasp how the heart rhythm is synchronized and why disturbances in this process can lead to arrhythmias.