Pathophysiology
Clinical meaning
Heart sounds are produced by the closure of valves and the turbulence of blood flow. Understanding the hemodynamic events that produce each sound is essential for clinical assessment. Normal Heart Sounds: • S1 ('Lub'): Closure of the AV valves (mitral and tricuspid) at the BEGINNING of systole. Best heard at the apex (mitral area: 5th ICS, left MCL). S1 marks the onset of ventricular contraction. Louder in mitral stenosis (valve leaflets are stiff and snap shut forcefully), softer in mitral regurgitation (incomplete closure). • S2 ('Dub'): Closure of the semilunar valves (aortic and pulmonic) at the END of systole / beginning of diastole. Best heard at the base of the heart (2nd ICS). A2 (aortic closure) normally precedes P2 (pulmonic closure): this creates physiologic splitting that widens during inspiration (increased venous return delays RV ejection and pulmonic valve closure). Extra Heart Sounds: • S3 (Ventricular Gallop): Low-pitched sound heard in early diastole, immediately after S2. Caused by rapid passive filling of a volume-overloaded or dilated ventricle. Sound of blood 'sloshing' into an overfilled ventricle. Best heard with BELL at apex,...