Thoracic vein aneurysms are very rare vascular lesions, usually detected as incidental findings. We describe the case of a patient with an advanced atrioventricular block who underwent definitive pacemaker implantation. In order to explain the difficult advancement of a pacemaker lead, vein angiography was performed during the procedure and a large innominate vein aneurysm was observed. Successful lead placement was then performed without further complications. (PACE 2008; 31:627-629)