OBJECTIVE--To determine the need for long-term pacing and optimum mode of pacing in cardiac transplant recipients. DESIGN--(a) A retrospective review of patient records. (b) A prospective study of pacemaker use by 24 hour ambulatory electrocardiography before and after reprogramming to minimise use of pacemakers. SETTING--Outpatient clinic, supra-regional cardiopulmonary transplant unit. PATIENTS--All 21 patients at this centre who had received permanent pacemakers after cardiac transplantation. 18 of 19 survivors completed the prospective part of the study. MAIN OUTCOME MEASURE--The presence of pacing during a 24 hour ambulatory electrocardiographic recording (programming: 50 beats/min, rate sensor inactivated). RESULTS--21 of 191 (11%) recipients surviving one month or more received permanent pacemakers. The indication was sinus node dysfunction in 13 (62%) and atrioventricular (AV) block in eight (38%). Patients who paced on follow up 12 lead electrocardiograms declined from 38% at three months to 10% at three years after transplantation. After programming to 50 beats/min only five of 18 (28%) patients paced during a 24 hour ambulatory recording. Four of 11 (36%) recipients who received pacemakers for sinus node dysfunction paced compared with one of seven patients (14%) paced for AV block. No patient who had a pacemaker before the 16th day after operation continued to pace whereas five of nine implanted later were used long-term. CONCLUSION--Only five of 18 (28%) patients with pacemakers continued to pace long-term. Continued pacing was more common in those with persistent sinus node dysfunction after the second week after operation but the need for long-term pacing was not predictable.