Abstract Patients with coarctation of the aorta (CoA) who previously underwent successful surgery are often diagnosed on standard electrocardiograms as having partial right bundle branch block. After surgery 24 patients with CoA had body surface potential mapping (BSPM) with the Case Western Reserve University 180 electrode system; of these 7 had additional aortic stenosis and none had ever had intracardiac communication. The average age at the initial surgery for CoA was 4.0 ± 3.3 years and at the time of the BSPM it was 12.7 ± 5.9 years. For the 17 patients with CoA without aortic stenosis the average age at the initial surgery was 5.0 ± 3.4 years and at the time of the BSPM it was 14.2 ± 6.0 years. In 11 of the 24 patients, a cardiac catheterization was performed, and each patient demonstrated normal pulmonary artery and right ventricular systolic pressure except for one child with 40 mmHg systolic. In the others all indications were that right ventricular pressure was normal. In 11 of the 24 patients, congestive heart failure had been present in infancy. All 24 cases had evidence for epicardial right ventricular breakthrough on the BSPM, a finding believed to indicate right ventricular activation from endocardium to epicardium via the normal Purkinje system. There were no findings on the BSPM suggesting that right bundle branch block was present. Right ventricular hypertrophy with or without terminal right conduction delay was present on the BSPM in 19 of the 24 patients (9 with additional left ventricular hypertrophy—left ventricular hypertrophy alone in 5). Right ventricular hypertrophy could be considered in 6 of 19 patients in the electrocardiogram, and in 11 of 19 in the vectorcardiogram. The mechanism for the persistent electrocardiographic right ventricular hypertrophy is postulated to involve right ventricular hyperplasia in utero or in early neonatal life, which never disappears.