<prompt> 2nd heart sound is due to-Closure of AV valvesClosure of aortic valveInthrushing of bloodAtrial contraction  <response>: Ans. is b i.e., Closure of aortic valve 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 sec.0.1 sec.-Frequency25-45 Hz50 Hz-20HzrCauseSudden closure of mitral tricuspid valvesClosure of aortic pulmonary valvesRapid ventricular fillingr due to inthru- sing of blood from atriaVentricular filing due to atrial contraction causing inthrushing of blood.TimingStart of ventricular systoleJust after end of ventricular systoleBegining of middle third of diastoleImmediately before 1st heart sound presystolicHeardS1 S2 can be heard with stethoscopeS3 S4 can not be heard by stethoscope ear. So oftenly and Ss sometimes can be recorded in phonocardiorgam 