During which phase of the cardiac cycle does the first heart sound take place?

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Phase of isotonic relaxationPhase of isovolumetric relaxationPhase of isovolumetric contractionPhase of isotonic contractionPhase of rapid ventricular filling

Explanation

The first heart sound (S1) is produced during the isovolumetric contraction phase, when the ventricles contract with no volume change, causing the atrioventricular valves to close. This distinguishes it from other phases like isotonic relaxation or isovolumetric relaxation.