Third heart sound

This is heart sound is caused by rapid ventricular filling in early diastole. Third heart sound may be divided into left ventricular (LV) third heart sounds and right ventricular (RV) third heart sounds.

Note that an early third heart sound may occur in constrictive pericarditis.

Clinical features:

• louder at the apex and the left sternal edge
• if right ventricular then louder on inspiration
• if left ventricular then louder on expiration

Evidence base:

• in patients referred for non-emergency left sided heart catherisation, third and fourth heart sounds detected by phonocardiography (1)
  • neither the phonocardiographic S3 nor the S4 is a sensitive marker of left ventricular dysfunction
  • the phonocardiographic S3 is specific for left ventricular dysfunction and appears to be superior to the moderate specificity of the phonocardiographic S4
• thus the absence of a gallop rhythm should not be used to indicate the absence of left ventricular dysfunction and certainly cannot replace other diagnostic testing when screening for left ventricular dysfunction

Reference:

1. Marcus GM et al. Association between phonocardiographic third and fourth heart sounds and objective measures of left ventricular dysfunction. JAMA 2005; 293:2238-44.
2. Commentary. Evidence-Based Medicine 2005;10:182.