Microprocessor-controlled antitachycardia pacemaker expand the automatic detection of the tachycardia and incorporate multiple, different termination modes. We report our results in the long-term therapy of paroxysmal supraventricular tachycardia with the antitachycardia pacemaker "Tachylog 651". The system was implanted in 10 patients with a mean age of 48 years (from 20 to 68 years): Wolff-Parkinson-White syndrome 4 patients, paroxysmal AV nodal reentrant tachycardia 6 cases. The rate of the reentrant tachycardia was 162 +/- 23/min. The system reliably differentiated between paroxysmal supraventricular tachycardia and sinus tachycardia, including 4 patients with a tachycardia rate of less than 150/min. Burst overdrive pacing was effective in 6 patients and the "self-search system" in 3 patients. During follow-up of 9 +/- 4 months 104 +/- 93 successful interventions per patient were observed; change of the termination mode became necessary in 4 patients and of the detection mode in 3 patients. The incorporation of programmable detection and multiple termination modes in the microprocessor-controlled antitachycardia systems allows the effective long-term antitachycardia pacing. The multiprogrammable "Tachylog 651" pacemaker is an advancement in the electrotherapeutic treatment of paroxysmal supraventricular tachycardias, including the automatic treatment of tachycardias with low rates.