The Medtronic VALIANT Thoracic Stent Graft with Xcelerant Delivery System is designed to treat diseases of the descending thoracic aorta including but not limited to aneurysms and dissections. The VALIANT Stent Graft is designed to exclude the aneurysm, the false lumen or site of rupture and restore the blood flow through the stent graft lumen. The device is intended for use either in patients who are candidates for conventional surgical repair, and in patients who are not candidates for conventional surgical repair due to pre-existing risk factors.