Valve Timing in Cardiac Cycle Pressure Graph

Steps:

• Examine pressure curves: W occurs when ventricular pressure rises above atrial, closing AV valves.
• X follows as ventricular pressure exceeds arterial, opening semilunar valves.
• Y marks ventricular relaxation where pressure falls below arterial, closing semilunar valves.
• Z happens when atrial pressure surpasses ventricular, opening AV valves.

Why C is correct:

• Matches cardiac cycle physiology: AV valves close (W) at ventricular systole onset; semilunar open (X) during ejection; semilunar close (Y) at end of systole; AV open (Z) for ventricular filling.

Why the others are wrong:

• A: Y is semilunar closure, not opening.
• B: X is semilunar opening, not closure; Y is closure, not opening.
• D: X is semilunar opening, not closure; Y is closure, not opening.

Final answer: C