BACKGROUND: The improvement of surgical techniques and the use of immunosuppressive drugs within the past 15 years has made heart transplantation an increasingly performed procedure and an accepted treatment for end-stage cardiac failure. HYPOTHESIS: The aim of this study was to describe the changes of the 12-lead electrocardiogram (ECG) after heart transplantation and to determine their prognostic value on complications such as rejection or graft coronary artery disease during follow-up. METHODS: The ECGs of 62 consecutive patients were analyzed for 5 years at follow-up periods of 1, 2, 3, 6 months and yearly after transplantation. RESULTS: The most prevalent abnormality was the presence of complete or incomplete right bundle-branch block (RBBB). New RBBB appeared in 69% (43/62) of the patients, mainly during the first month (21/43). There was no left bundle-branch block. We detected nine episodes of supraventricular arrhythmias: one atrial fibrillation, six atrial flutter, one junctional tachycardia, one orthodromic tachycardia on a Wolff-Parkinson-White syndrome; all appearing during the first 3 months. Three of the six episodes of atrial flutter occurred during an episode of acute rejection. There was no relation between RBBB and the gender and age of recipients and donors, nor with the graft ischemic time and the pretransplantation hemodynamic values. Right bundle-branch block was not associated with acute rejection nor with graft coronary artery disease. CONCLUSION: The ECG abnormalities after heart transplantation have no predictive value on the long-term evolution. Right bundle-branch block is very frequent and is not associated with adverse prognosis.