Heart sounds

1st heart sound

• Closure of mitral and tricuspid valves at the start of ventricular systole

2nd heart sound

• Closure of aortic and pulmonary valves just after the end of ventricular systole
• Aortic valve closes before pulmonary valve
  * especially during inspiration

3rd heart sound

• 1/3 of the way through diastole
• Probably due to rapid ventricular filling
• Heard in some normal young people

4th heart sound

• Just before the first heart sound
• Due to ventricular filling
• Heard when atrial pressure is high or ventricle is stiff
• Rarely heard in normal adults