During what phase of the cardiac cycle does the heart fill with blood?

In the cardiac cycle, the heart fills with blood primarily during the diastole phase. Diastole is the period when the heart muscle relaxes after contraction, allowing the chambers of the heart, particularly the ventricles, to expand and fill with blood coming from the atria.

During this phase, the pressure in the heart decreases, causing the atrioventricular valves (the mitral and tricuspid valves) to open, which facilitates blood flow from the atria into the ventricles. The filling occurs passively at first as the blood flows into the ventricles, and then actively when the atria contract towards the end of diastole, pushing additional blood into the ventricles.

This process is crucial for ensuring that the heart has enough blood volume to pump effectively in the next phase, which is systole, where the heart contracts and pumps blood out into the circulation. Understanding diastole’s role in cardiac filling is fundamental to grasping the overall mechanics of heart function and hemodynamics.