The usual morphology for paced events originating from the right ventricle has a left bundle branch block (BBB) pattern. However, in a few patients, right BBB configurations are identified. It is important to differentiate safe right BBB patterns from those caused by septal or free wall perforation. Paced electrocardiograms were examined in 179 consecutive patients who underwent pacemaker placement. Fourteen patients (8%) were identified with right BBB configurations. Posteroanterior and lateral chest radiographs and echocardiograms were evaluated specifically to identify the pacing lead location in this group. In addition, 152 paced episodes from published reports were combined with our population to create an electrocardiographic algorithm differentiating right ventricular septum, right ventricular apex, coronary venous, and left ventricular pacing. Chest radiographs and echocardiographic lead locations correlated perfectly in the 11 patients available for echocardiograms. With use of a left superior axis and precordial transition by lead V₃, right ventricular right BBB morphologies were correctly detected in 18 of 21 patients (86% sensitivity, 99% specificity) and appropriately separated from left ventricular pacing in 18 of 19 patients (95% positive predictive value). Therefore, 12-lead electrocardiograms are a rapid, reliable means of separating right and left ventricular right BBB pacing morphologies. Prudent use of these criteria will help eliminate unnecessary echocardiography, anticoagulation, and lead revision.