A dual-chamber pacemaker was implanted in a 69-year-old man. As far as the surgeon was concerned, there were no problems with implantation via a left subclavian transvenous route. The location of the leads seemed to be correct under the fluoroscope. Stimulation thresholds were correct. The chest radiograph was initially considered not revealing anomaly and the position of the electrodes was described as: "ends of leads appear to be correctly placed". On performing precise checks on the pacemaker, the ECG had the appearance of complete right bundle-branch block, during ventricular stimulation, a reason for fearing malpositioning in the left ventricle. The chest X-rays (A) were re-examined. On the lateral X-ray, the lower part of the ventricular lead has a first posterior small kink and is then distinctly directed anteriorly but its end remains clearly distant from the anterior surface. Was it still correctly positioned in the right ventricle? An ultrasound examination (B) was performed: the lead passed from the right atrium to the left atrium through the inter-atrial septum at the foramen ovale (arrow) then it penetrated the left ventricle through the mitral valve (arrow head). Despite the ambiguous appearance of the chest X-rays at the beginning, this lead was therefore malpositioned. A thoracic scan (C) was performed for another indication and also clearly showed the stimulation lead in the left atrium then the left ventricle.