Valve positions during ventricular contraction

Steps:

• Chambers X and Y are the ventricles, which contract simultaneously during systole.
• Ventricular contraction increases pressure, closing atrioventricular (AV) valves to prevent backflow into atria.
• High ventricular pressure exceeds arterial pressure, opening semilunar valves to eject blood into pulmonary artery and aorta.
• Valves 1 and 4 are AV (tricuspid and mitral), closing; valves 2 and 3 are semilunar (pulmonary and aortic), opening.

Why A is correct:

• It matches ventricular systole: AV valves (1, 4) closed, semilunar valves (2, 3) open, per heart physiology preventing backflow and enabling ejection.

Why the others are wrong:

• B: Incorrectly shows valve 1 open (AV valves must close) and valve 4 open (semilunar should open, but pattern mismatches).
• C: Wrongly has valve 1 open (AV closes) and valve 3 closed (semilunar opens).
• D: Erroneously shows valves 1 and 3 closed (valve 3 as semilunar must open) and valve 4 open (AV closes).

Final answer: A