|First heart sound|
- Due to closure of atrioventricular (Mitral,Tricuspid) valves simultaneously.
- Long, soft and low pitched and sounds like LUBB
- Produced during isometric contraction and earlier part of ejection period
|Second heart sound|
- Due to closure of semilunar (Pulmonary, aortic) valves simultaneously.
- Short, sharp, high pitched and sounds like DUBB.
- Produced during the onset of diastole
|Third heart sound||Produced during rapid filling period and is inaudible by stethoscope|
|Fourth heart sound||Produced during atrial systole and is inaudible.|
[Sembulingam 4th ed 501/ 5th ed 524]