(A) ECG showing ventricular tachycardia induction by a premature ventricular contraction (*). (B) ECG showing monomorphic ventricular tachycardia (130 bpm) before the infusion of isoproterenol. (C) ECG after the infusion of isoproterenol showing a more rapid (200 bpm) ventricular tachycardia with a narrower QRS.