This is a graphic example of a second heart sound that is split in expiration and single in inspiration. This is called paradoxic splitting of S2. This occurs when there is substantial delay in the aortic closure sound causing A2 to occur after P2. As a result of this delay of A2, normal inspiratory delay of P2 causes P2 to move toward A2, thereby narrowing or eliminating splitting. Conditions that can cause paradoxic splitting of S2 include severe left ventricular outflow tract obstruction, as in hypertrophic cardiomyopathy and left bundle branch block.