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Heart sounds (first, soft)

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Possible causes of a soft first heart sound include:

  • early atrioventricular closure (in this situation the leaflets are semi-closed at the end of diastole)
    • a low flow at the end of diastole
    • a P-R interval that is greater than 0.2 s
  • a rigid calcified valve will cause a soft first heart sound
  • if the left ventricle is not contracting efficiently then there may be a soft first heart sound produced
  • a delayed onset of left ventricular systole

Hence, causes include:

  • mitral regurgitation
  • low blood pressure, for example with M.I.
  • rheumatic carditis
  • severe heart failure
  • left bundle branch block

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