What happens to the AV valves during isovolumetric contraction?

During isovolumetric contraction, the atrioventricular (AV) valves close in response to the rising pressure within the ventricles as they begin to contract. This closure of the AV valves is crucial as it prevents backflow of blood into the atria and ensures that the blood is directed toward the outflow tracts to the aorta and pulmonary arteries once the pressure exceeds that of the respective vessels.

The closure of the AV valves generates the first heart sound (S1), which is a key indicator of the cardiac cycle's transition from diastole to systole. This event is significant because it marks the beginning of ventricular contraction as the heart prepares to eject blood into circulation.

In contrast, the other options describing the behavior of the AV valves during this phase do not align with the physiological process. The AV valves do not open during isovolumetric contraction nor remain open, as this would allow blood to flow backward into the atria. Furthermore, the idea that they are "pulled tight without closure" does not accurately convey the important function of the valves, which is to effectively seal off the atria from the ventricles during this phase of contraction. Thus, the closure of the AV valves during isovolumetric