The atrioventricular valves are the mitral and tricuspid valves. During which phase are these valves open?

• A. Diastole
• B. Atrial Systole
• C. Isovolumetric Contraction
• D. Ejection

Answer: (A)

The key idea is that the atrioventricular valves open when the atrial pressure is higher than the ventricular pressure, allowing blood to flow from the atria into the ventricles as the ventricles fill. This happens during the heart’s relaxation phase—diastole—when the ventricles are not pumping and are instead filling with blood. Early in diastole, blood moves through the open AV valves into the ventricles, and toward the end of diastole, the atria contract to push any remaining blood into the ventricles, still with the AV valves open.

In contrast, the AV valves are closed during isovolumetric contraction (when the ventricles contract but the valves are shut) and during ejection (when the ventricles push blood into the aorta and pulmonary trunk while the AV valves remain closed to prevent backflow).