Valve States During Isovolumetric Relaxation

Steps:

• In the cardiac cycle, semilunar valves close when ventricular pressure falls below arterial pressure.
• This occurs at the start of ventricular diastole, initiating isovolumetric relaxation.
• During this phase, atrioventricular valves remain closed because atrial pressure has not yet exceeded ventricular pressure.
• Thus, both atrioventricular and semilunar valves are closed when right ventricular pressure is lower than pulmonary artery pressure.

Why C is correct:

• Isovolumetric relaxation requires both valve sets closed to prevent backflow while ventricular pressure equalizes with atrial pressure (definition of the phase).

Why the others are wrong:

• A: Semilunar open requires ventricular pressure > arterial pressure (ejection phase).
• B: Atrioventricular open occurs later in diastole when ventricular pressure < atrial pressure (filling phase).
• D: Both open simultaneously never happens, as it would allow bidirectional flow and disrupt pressure gradients.

Final answer: C