The second heart sound is heard during which phase of the cardiac cycle?

• A. Isovolumetric contraction
• B. Ventricular filling
• C. Ventricular ejection
• D. Isovolumetric relaxation

Answer: (D)

Verified step by step guidance

1. Understand the cardiac cycle phases: The cardiac cycle consists of several phases, including isovolumetric contraction, ventricular filling, ventricular ejection, and isovolumetric relaxation.
2. Identify the events associated with heart sounds: The first heart sound (S1) is associated with the closure of the atrioventricular valves (mitral and tricuspid) during the beginning of ventricular contraction. The second heart sound (S2) is associated with the closure of the semilunar valves (aortic and pulmonary) at the end of ventricular ejection.
3. Focus on the second heart sound (S2): The second heart sound occurs when the semilunar valves close, marking the transition from ventricular ejection to isovolumetric relaxation.
4. Relate the second heart sound to the cardiac cycle phase: Since the semilunar valves close at the end of ventricular ejection, the second heart sound is heard during the isovolumetric relaxation phase.
5. Conclude the relationship: The second heart sound is heard during the isovolumetric relaxation phase of the cardiac cycle, as this is when the semilunar valves close, leading to the sound.