Pacemakers are playing an increasing role in the management of patients with tachycardia. Pacing to prevent tachycardia must be differentiated from pacing to terminate tachycardia. Pacing is of proven value in preventing ventricular tachycardia that occurs in the setting of complete heart block or the setting of drug-induced QT interval prolongation and may be valuable in some other patients with nonsustained ventricular tachycardia. Pacing termination has found its greatest use as an alternative to cardioversion in patients with atrial flutter, especially those with suspected digitalis toxicity or sick sinus syndrome or patients after cardiac surgery. Implanted pacemakers that can be activated by the patient are a promising area or investigation for the termination of tachycardias that are recurrent and debilitating despite medical therapy.