<prompt> S2 is associated with -Rapid ventricular fillingAtrial contractionClosure of semilunar valvesClosure of AV valves  <response>: Ans. is c i.e., Closure of semilunar valves o S, is due to closure of semilunar valves aortic and pulmonary valves.Feature1st heart sound2nd heart sound3rd heart sound4th heart soundCharacterLow pitched frequency slightly prolonged lubShorter high pitched dupSoft low pitched weak rumblingArterial heart soundDuration0?14 second0?11 second0?1 second-Frequency25-45 Hz50 Hz-20HzQCauseSudden closure of mitral tricuspid valvesClosure of aortic pulmonary valvesRapid ventricular fillingQ dt inthrusing of blood from atriaVentricular fillingQ dt atrial contraction causing inthrushing of blood.TimingStart of ventricular systoleJust after end of ventricular systoleBegining of middle third of diastoleImmediately before 1st heart sound presystolicHeardS.1 S2 can be heard with stethoscopeS1 S4 can not be heard by stethoscope ear Q. So oftenly and S5 sometimes can be recorded in phonocardiorgam 