Which chamber of the heart relaxes during ventricular systole?

During ventricular systole, the ventricles contract to pump blood out of the heart, specifically into the pulmonary artery and the aorta. As the ventricles contract, the pressure within the ventricles rises significantly, which necessitates the relaxation of the atria. This relaxation is crucial because it allows the atria to refill with blood returning from the body and lungs, preparing for the next cycle of contraction during the subsequent diastole.

This coordination ensures that the heart functions efficiently; while the ventricles are actively ejecting blood, the atria are in a filling phase, ready to push blood into the ventricles during the next heartbeat. Thus, the atria must relax during ventricular systole to facilitate this process effectively.