Pathophysiology
Clinical meaning
Heart sounds are produced by the closure of cardiac valves during the cardiac cycle. S1 (lub) occurs when the mitral and tricuspid valves close at the beginning of systole, and S2 (dub) occurs when the aortic and pulmonic valves close at the beginning of diastole. S3 may indicate heart failure in adults due to rapid ventricular filling against a non-compliant ventricle. S4 represents atrial contraction against a stiff ventricle, often associated with ventricular hypertrophy. Murmurs result from turbulent blood flow across abnormal valves, septal defects, or increased flow states. Auscultation requires systematic listening at all valve areas using both the bell (low-pitched sounds) and diaphragm (high-pitched sounds).