Interactive Guide to Physical Examination

The Third and Fourth Heart Sounds

The third heart sound:

  • Often is a benign finding in children, adolescents, and young adults.
  • Rarely is heard after age 40 as a normal finding.
  • Follows closely after S2, during the rapid filling wave in diastole.
  • Is a low frequency sound, best heard with the bell of the stethoscope pressed lightly to the apex, with the patient in the left lateral decubitus position.
  • Is most audible at the beginning of expiration.

The exact genesis of the third heart sound is controversial but is thought to be the result of a complex interaction between blood and the ventricular wall during ventricular filling. The most common cause of a pathologic S3 is ventricular dysfunction with the resultant increased end diastolic and end systolic volume in the ventricle.

The fourth heart sound:

  • Occasionally is heard in healthy individuals.
  • Most commonly is a pathologic finding.
  • Occurs just before S1, coincident with atrial contraction, and is never heard in the absence of atrial contraction.
  • Is a low frequency sound, heard best with the bell applied lightly to the chest wall along the lower left sternal border with the patient in the left lateral decubitus position.
  • May increase with inspiration.

The exact genesis of S4 is controversial but it appears to be related to an increased resistance to ventricular filling during atrial contraction. An S4 can be heard in several pathologic condition.

View interactive module Click on the interactive icon to practice listening to S3 and S4.