Sound is that of paradoxical splitting, ie, S1–P2–A2 at rest (“out”) and S1–S2 with inspiration (“in”). Left bundle branch block delays aortic valve closure, so that split is audible at rest; inspiration decreases intrathoracic pressure, drawing more blood into the right ventricle and postponing pulmonic valve closure until it is superimposed on A2 and splitting becomes inaudible.