Heart sounds (first, loud)

A loud first heart sound occurs when the leaflets are wide open at the end of ventricular diastole and shut forcefully at the beginning of ventricular systole.

Possible causes of a loud first heart sound include:

• late atrioventricular closure
  • this occurs when there is rapid flow at the end of diastole e.g. mitral stenosis, the short diastole of tachycardic states and left to right shunts
  • where the P-R interval is less than 0.12 s. This situation results in an opened valve that is not closed at the time of ventricular contraction.

Hence:

• atrial fibrillation
• short diastole - tachycardia
• atrial premature beat
• mitral stenosis where high left atrial pressure delays mitral valve closure