What happens during systole of the heart?

During systole, the primary event is the contraction of the ventricles, which is crucial for pumping blood out of the heart. This phase is characterized by the generation of pressure in the ventricles that propels blood into the pulmonary artery and aorta. As the ventricles contract, the atria are in a filling phase, allowing them to replenish their blood volume in preparation for the next heartbeat.

The filling of the atria during this time is important because it ensures that when the ventricles finish contracting and enter diastole, enough blood is present to fill the ventricles for the next cycle of contraction. This efficient timing between the chambers maximizes cardiac output and maintains proper circulation throughout the body. Thus, the correct description of systole is that the ventricles contract while the atria are filling with blood.