What occurs during the rapid filling phase of the cardiac cycle?

During the rapid filling phase of the cardiac cycle, the key process involves blood rushing from the atria into the ventricles. This phase occurs shortly after the atrial contraction and the atria are filled with blood from the pulmonary veins (on the left) and the vena cava (on the right). When the atrioventricular (AV) valves (the mitral and tricuspid valves) open, there is a swift influx of blood into the ventricles due to the pressure gradient between the atria and ventricles. This phase is critical for ensuring that the ventricles receive an adequate volume of blood before the next contraction.

The other options describe events that are not accurate during this specific phase of the cardiac cycle. For example, ventricular contraction occurs during a different phase called isovolumetric contraction, while the AV valves are open during the rapid filling phase. The heart is not completely relaxed at this time, as the atria are actively contracting to push the last bits of blood into the ventricles just before the rapid filling begins. Understanding these phases and the sequence of events contributes to a comprehensive knowledge of cardiac mechanics and the overall cardiac cycle.