The electrocardiogram is often abnormal after orthotopic cardiac transplantation. This study was conducted in order to evaluate the frequency of these abnormalities in a population of 29 patients transplanted according to the conventional mode or the total mode. We also investigated the correlation between these abnormalities and the presence of left ventricular hypertrophy or deviation of the left ventricular long axis. The left ventricular mass was measured by TM echocardiography. The position of the left ventricular long axis was determined by MR on a ultrarapid sequence. The ECG was normal in 5 patients. The abnormalities revealed in the other 24 patients were: an rSr' or rsr' appearance in V1 with a QRS complex less than 0.12 sec in 11 patients, complete right block in 1 patients, repolarization abnormalities (apart from those associated with branch blocks) in 8 patients, left axis deviation of the QRS in 5 patients, a biphasic P wave in V1 with a Morris index greater than 4 mV.sec in 5 patients, and double atrial activity in 3 patients. These abnormalities were observed regardless of the type of transplantation, with the exception of double atrial activity which was only observed in the group of patients undergoing conventional transplantation. On average, the long axis of the left ventricle was more horizontal and deviated to the left compared to age- and sex-matched controls. All patients with left axis deviation of the QRS had left ventricular hypertrophy versus 13 of the 24 patients without QRS axis deviation and abnormalities of position of the anatomical left ventricular long axis. Our results therefore suggest that the frequent presence of right branch block in heart transplant recipients is due to factors other than the position of the heart in the thorax, for example right ventricular hypertrophy.