heart sounds (first, soft)

Last reviewed 01/2018

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