The murmur produced by an ASD is due to increased flow through the pulmonic valve, thus it is remarkably similar to that of pulmonic stenosis. The difference lies in the intensity and splitting pattern of the S2 heart sound. The intensity of S2 should remain unchanged and may in fact be accentuated if pulmonary hypertension develops. The S2 is fixed-split in a person with an ASD. This differs from the widened split S2 seen in severe pulmonic stenosis. Also, the murmur of an ASD does not increase in intensity with inspiration like that of pulmonic stenosis.

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