The Second Heart Sound
July 1st, 2020
Overview
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
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On Expiration
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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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