During the cardiac cycle, when do the AV valves open and how does this relate to ventricular filling?

• A. AV valves open during systole, allowing ventricular filling.
• B. AV valves open during diastole, allowing rapid ventricular filling, followed by diastasis; they close at onset of systole to prevent backflow.
• C. AV valves close during diastole to prevent backflow.
• D. AV valves open at the onset of systole to facilitate diastolic filling.

Answer: (B)

Opening of the AV valves happens during diastole when atrial pressure is higher than ventricular pressure, allowing blood to flow from the atria into the ventricles. Early in diastole, this results in rapid ventricular filling as the ventricles relax and accommodate incoming blood. As filling progresses, the pressure gradient narrows, leading to a slower phase called diastasis, during which atrial contraction (the atrial kick) adds the remaining volume to the ventricle. The AV valves then close at the onset of systole when ventricular pressure rises above atrial pressure, preventing backflow into the atria.