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Two components

• S2 is best heard at right and left sternal edges in the second intercostal spaces where it should be louder than S1.
• A2 normally precedes P2.
• Each component occurs earlier with reduced, and later with increased capacitance of the corresponding vascular bed.
• With normal breathing, S2 widens with inspiration then narrows and closes with expiration.
• May have to listen with patient sitting if splitting seems persistent at end-expiration.

Normal, physiologic splitting of S2

• Inspiration increases capacitance of the pulmonary vascular bed, delays the pulmonary artery dicrotic incisura and delays the pulmonic component of the second sound. Expiration has opposite effect.
• Second sound splitting widens with inspiration.
• Second sound becomes single (<0.03 sec) at end-expiration (patient may have to stand)