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Cardio Exam

The Second Heart Sound

July 1st, 2020


The second heart sound (S2) indicates closure of the aortic (A2) and pulmonary (P2) valves.
The second heart sound normally splits on inspiration and is single during expiration, and A2 (closure of the aortic valve) is louder than P2 (closure of the pulmonary valve), even in the pulmonary area.
  • On Inspiration

  • On Expiration

Soft A2

  • Listen For

  • Loss of normal splitting of S2 on inspiration, due to a soft or absent A2.
  • Causes of Soft A2

  • Severe aortic stenosis
  • Severe aortic regurgitation

Loud P2

  • Listen For

  • P2 louder than A2 in the pulmonary area.
  • Causes of Loud P2

  • Pulmonary hypertension
  • Atrial septal defect

Wide Splitting of S2

  • Listen For

  • Widening of the normal splitting of S2 on inspiration.
  • Causes of Wide Splitting of S2

  • Mitral regurgitation
  • Pulmonary stenosis
  • Right bundle branch block

Paradoxical Splitting of S2

  • Listen for

  • A single S2 during inspiration and split S2 during expiration, due to P2 occurring before A2.
  • Causes of Paradoxical S2 Splitting

  • Severe aortic stenosis
  • Left bundle branch block
  • Hypertrophic obstructive cardiomyopathy
  • Patent ductus arteriosus
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