Answer: Ok Diastole commences with the closure of the aortic and pulmonary valves. Intraventricular pressure falls but there is very little increase in ventricular volume (isovolumetric relaxation). Once ventricular pressure falls below atrial pressure, the mitral and tricuspid valves open and ventricular filling begins.The first heart sound (S1) is produced by vibrations generated by closure of the mitral (M1) and tricuspid valves (T1). It corresponds to the end of diastole and beginning of ventricular systole and precedes the upstroke of carotid pulsation.
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