This lesson covers physiologic and paradoxical splitting of the second heart sound. As described earlier, the second heart sound is produced by the closing of the aortic valve and the closing of the pulmonic valve. These valves can close at slightly different times. This creates a split second heart sound. The second heart sound's splitting and intensity can indicate several types of cardiac abnormalities. In this recording, the splitting varies between zero and eighty milliseconds. The variation in splitting is a function of the respiratory cycle. In physiologic splitting the maximum separation between aortic and pulmonic components of the second heart sound occurs at peak inspiration. In paradoxical splitting the maximum separation occurs at peak expiration. Paradoxical splitting can occur with aortic stenosis and left bundle-branch block. Both of these abnormalities cause a delay in the aortic valve closure until after the pulmonic valve closure, reversing the normal sequence of events.