Sixteen patients with recurrent, drug-resistant supraventricular (13 patients) or ventricular (3 patients) tachycardia were treated chronically by programmable extrastimulus pacing; either a fully automatic device (Telectronics PASAR 4151: eight patients with supraventricular tachycardia) or a patient--activated device (Medtronic Interactive Tachy System) was used. During a follow-up period of 5 to 30 months, five of the subjects treated with the fully automatic device showed successful results, one had recurrent tachycardia, and two had their units explanted for system-related problems. The patients treated with the externally activated device were, on the whole, very well controlled. This mode of treatment, if applied in well-selected cases, is promising; it seems safe and considerably reduces the number of hospital admissions.