The 12-lead scalar electrocardiograms of heart transplant recipients were examined prior to hospital discharge (N = 191), and at 1 (N = 162), 2 (N = 97), and 3 years (N = 46) after transplantation. At the pre-discharge point, 46% had right bundle branch block (RBBB) QRS morphology (QRS duration greater than or equal to 120 msec: 20 patients, less than 120 msec: 67 patients). This finding tended to be manifest on the first day following transplantation; its prevalence remained constant over 3 years of follow up. Rejection, ischemic time, preoperative pulmonary vascular resistance, and donor age were not associated with the presence of RBBB morphology. A subgroup of 46 consecutive patients (21 with RBBB morphology) underwent right-sided heart catheterization and radionuclide angiography prior to discharge. RBBB morphology was not associated with any hemodynamic abnormality at catheterization. Based on the radionuclide study, RBBB morphology was associated with a greater left anterior oblique angle required for the best visual separation of the ventricles during acquisition of the study (angle of interventricular septal plane to sagittal plane: 69 +/- 11 versus 59 +/- 9 degrees; p = 0.019), and with the presence of right ventricular dysfunction (13 of 21 versus 6 of 25 patients; p = 0.009). The high prevalence of RBBB morphology in heart transplant recipients appears to be related to posterior rotation of the long axis of the heart in the transverse plane, probably resulting from the surgical technique, and to right ventricular dysfunction.