split first (1st) heart sound

Last reviewed 01/2023

The differential contraction of the left and right ventricle causes a splitting of the first heart sound.

An abnormally large splitting of the first heart sound is heard when there are:

  • either conduction abnormalities:
    • right bundle branch block
    • pacing from an electrode on the LV
    • left ventricular ectopics

  • or mechanical causes:
    • Ebsteins anomaly
    • atrial septal defect
    • tricuspid stenosis


  • Kirby B (1993).Clinical examination of the heart. Medicine International, 21(8), 294-99.