A case of persistent left fifth aortic arch, forming a congenital ``double-lumen'' aortic arch, has been diagnosed on angiocardiography during life. It appeared as an unusual vascular structure running inferiorly and parallel to the ``real'' aortic arch from the innominate artery to the left subclavian artery superior to the pulmonary artery. This anomaly was found in the setting of tetralogy of Fallot, an association never described before, with patent ductus arteriosus (previously reported in most cases). The left aortic arch in this case was not a source of pulmonary circulation, as described in previous cases with pulmonary atresia and ventricular septal defect, but was a systemic-to-systemic connection without functional relevance.