Sinus node dysfunction may complicate heart transplantation in over 50% of cases, leading to prolonged bradyarrhythmias in 20% of recipients. Permanent pacemaker implantation, the standard treatment for such persistent rhythm disturbances, can result in significant complications in this setting. A protocol with theophylline, a methylxanthine known to reverse the sinus node electrophysiologic abnormalities observed in transplant patients, was initiated at our institution in October 1989 to treat posttransplantation bradyarrhythmias and to reduce the need for pacemaker implantation. Patients with sinus or nodal bradycardia or sinus arrest were given theophylline orally; the drug was initiated in 15 of 38 patients (39.5%), 3 to 24 days after transplantation. Mean duration of treatment was 57.4 days (range, 20 to 105 days). Normal sinus rhythm with a rate of more than 90 beats/min was restored in 14 of 15 patients (93.3%). Permanent pacing was required in one patient. Transplant recipients before October 1989 (group 1, n = 112) were compared with subsequent transplant recipients (group 2, n = 38). These groups did not differ significantly in incidence of bradyarrhythmias or potential risk factors for posttransplantation sinus node dysfunction, though a greater preoperative use of amiodarone occurred in group 2. Permanent pacemaker requirement was significantly reduced from 16.1% in group 1 to 2.6% in group 2 (p < 0.05) with the introduction of theophylline. Theophylline is effective treatment for posttransplantation bradyarrhythmias, thereby resulting in a reduced need for pacemaker implantation.