In a patient with severe left ventricular dysfunction resulting from chronic nonparoxysmal sinus tachycardia, rate control and improvement in left ventricular function were achieved with atrioventricular junction ablation and ventricular pacemaker implantation. Within 12 hours after the ablation procedure, several episodes of polymorphic ventricular tachycardia that may have been triggered by the abruptly decreased heart rate occurred. Recurrence of polymorphic ventricular tachycardia was prevented by an increase in pacing rate.