What characterizes Phase 2 of the cardiac action potential?

Phase 2 of the cardiac action potential is characterized by a plateau phase, where there is a significant influx of calcium ions into the cardiac cells. This phase follows the initial rapid depolarization phase (Phase 0) and each cardiac muscle cell contracts in response to the influx of these calcium ions.

The plateau is crucial because it prolongs the refractory period, preventing premature contractions and ensuring that the heart has adequate time to fill with blood before contracting again. This is essential for maintaining an effective and coordinated pumping action of the heart.

The mechanism involves various ion channels, specifically the L-type calcium channels, which open during this phase. This calcium influx sustained during Phase 2 allows for a prolonged contraction before repolarization occurs, contributing to the heart's ability to pump blood efficiently.