Valve Sequence in Cardiac Cycle

Steps:

• Atrial systole: AV valves open for ventricular filling.
• Ventricular systole starts: AV valves close (W), preventing backflow.
• Pressure rises: semilunar valves open (X) for ejection.
• Ventricular relaxation: semilunar valves close (Y), then AV valves open (Z) for filling.

Why B is correct:

• Matches the standard sequence where AV closure precedes semilunar opening, semilunar closure precedes AV reopening, per cardiac pressure dynamics.

Why the others are wrong:

• A: Places two AV events first, ignoring semilunar opening after AV closure.
• C: Starts with semilunar events, but AV closure initiates ventricular systole.
• D: Begins with semilunar and alternates incorrectly, reversing the systole-diastole transition.

Final answer: B