Exercise-Induced Left Bundle Branch Block Resulting in Severe Mitral Regurgitation.

Exercise hemodynamic catheterization is helpful to evaluate exertional symptoms when noninvasive investigations fail to provide an explanation in non-ischemic cardiomyopathy. In this case, a rate-related left bundle branch block resulted in severe dynamic mitral regurgitation and acute increase in pulmonary capillary wedge pressure. Cardiac resynchronization therapy resolved her symptoms. (Level of Difficulty: Intermediate.).