When does systole of the heart occur?

Systole refers to the phase of the cardiac cycle when the heart muscles contract, leading to the ejection of blood from the chambers of the heart. In this context, the correct answer indicates that systole occurs when the ventricles are contracting. During this contraction, blood is pumped out of the ventricles into the pulmonary artery and aorta, which is critical for maintaining circulation throughout the body.

As the ventricles contract, the atria are filling with blood from the veins, preparing for the next phase of the cardiac cycle, which is diastole. This distinction is essential because it highlights the dual functioning of the heart chambers during different phases, with the ventricles actively pumping blood while the atria serve as reservoirs. Understanding this relationship between contraction and filling helps to elucidate the hemodynamic functioning of the heart during systolic and diastolic phases.