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Recording provided by Jules Constant, MD.

Split 2nd Heart Sound in Left Bundle Branch Block
Sound is that of paradoxical splitting, ie, S 1 -P 2 -A 2 at rest (“out”) and S 1 -S 2 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 A 2 and splitting becomes inaudible.