Abnormal second heart sound Fixed splitting of the second heart sound 2017-12-17T16:08:14Z Fixed splitting of S2 Fixed splitting of S2 may occur in patients with secundum atrial septal defect. Lack of variation in the splitting between the two components of the second heart sound with respiration. Normally, the aortic valve closure (A2) is followed by the pulmonic valve closure (P2) but the A2-P2 interval increases with inspiration and decreases with expiration.