Transvenous pacemaker lead malposition in the left ventricle occurs rarely and requires a high index of suspicion for proper diagnosis. The case of a woman with unintentional lead placement in the left ventricle is presented. She had two episodes of transient neurologic deficits, possible secondary to embolic events, and was started on oral anticoagulants. Chest x-ray and electrocardiogram (ECG) suggested pacemaker lead malposition and transesophageal echocardiography revealed sinus venosus atrial septal defect. The lead was shown to cross the atrial septum and the mitral valve to the left ventricle. The malpositioned lead was successfully removed from the left ventricle at the time of surgical repair of the atrial septal defect. The potential value of 12-lead ECG, chest x-ray, posteroanterior and lateral views, and echocardiography in the diagnosis of pacemaker lead malposition are discussed and recommendations to avoid this complication at the time of pacemaker implant are outlined.