Physiology General 1d64ac37 First heart sound occurs during the: A Isovolumetric ventricular systole. B Isovolumetric ventricular diastole. C Protodisatole. D Ventricular ejection. High-Yield Explanation Isovolumetric ventricular systole is ended with the opening of the seminar valves, due to which first heart sound is produced.