First Heart Sound



  • The first heart sound (S1) indicates closure of the mitral and tricuspid valves.
  • S1 is normally heard best over the apex.
    • Causes of a Soft S1

    • Mitral regurgitation
    • Ventricular septal defect
    • First degree heart block
    • Left bundle branch block
    • Myocardial depression
    • Causes of a Loud S1

    • Mitral stenosis
    • Hyperdynamic circulation - exercise, infection, hyperthyroidism, pregnancy
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