Valve Positions Identify Cardiac Cycle Stages

Steps:

• During ventricular systole, high ventricular pressure closes atrioventricular (AV) valves and opens semilunar valves to eject blood.
• Diagram 1 shows closed AV valves and open semilunar valves, indicating ventricular contraction.
• Diagram 2 shows the same valve configuration, confirming ongoing ventricular systole.
• This matches both diagrams to ventricular systole, ruling out atrial involvement.

Why A is correct:

• Ventricular systole is defined by closed AV valves and open semilunar valves, directly matching the cross-sectional views in both diagrams.

Why the others are wrong:

• B: Atrial systole features open AV valves for atrial emptying; diastole has relaxed ventricles with open AV and closed semilunar valves.
• C: Diastole shows open AV valves and closed semilunar valves; atrial systole does not close semilunar valves.
• D: Atrial systole has open AV valves, not closed as in ventricular systole.

Final answer: A