The cardiac cycle is divided into seven phases.
The first phase begins with the P wave of the electrocardiogram, which represents atrial depolarization, and is the last phase of diastole.
Phases 2-4 represent systole, and phases 5-7 represent early and mid-diastole.
The last phase of the cardiac cycle ends with the appearance of the next P wave, which begins a new cycle.
> 022. Atrial Contraction (Phase 1)