During which phase do the AV and semilunar valves close and the first heart sound is heard, with ventricular pressure rising but no volume change?

During which phase do the AV and semilunar valves close and the first heart sound is heard, with ventricular pressure rising but no volume change?

• A. Isovolumetric contraction
• B. Ejection
• C. Isovolumetric relaxation
• D. End diastolic volume

Answer: (A)

During isovolumetric contraction, the ventricles begin to contract with all valves closed. The AV valves shut first, producing the first heart sound, while the semilunar valves are still closed, so ventricular pressure rises but there is no change in volume. When the ventricular pressure finally exceeds the pressure in the great arteries, the semilunar valves open and ejection begins.

During isovolumetric contraction, the ventricles begin to contract with all valves closed. The AV valves shut first, producing the first heart sound, while the semilunar valves are still closed, so ventricular pressure rises but there is no change in volume. When the ventricular pressure finally exceeds the pressure in the great arteries, the semilunar valves open and ejection begins.