S1, S2 and their significance
Normal heart sounds result from valve closure during the cardiac cycle.
S1 (Lub) - Closure of AV valves (mitral and tricuspid) at start of systole
S2 (Dub) - Closure of semilunar valves (aortic and pulmonary) at start of diastole
Clinical Note: S3 and S4 are abnormal in adults but may be normal in children. S3 suggests volume overload, S4 suggests reduced ventricular compliance.