The purpose of this study is to determine if the Valiant stent graft is safe and effective in treating patients who have a thoracic dissection. A thoracic dissection is a tear in the wall of the aorta, that causes blood to flow between the layers of the aorta and force the layers apart (dissect). This condition is a medical emergency and can quickly lead to death. Since stent grafting has been an effective way to treat other aortic conditions such as aneurysms (bulge in aorta wall), it is believed that the device would be effective in treating dissections. Information will be collected on the performance of the device for 5 years.

Inclusion Criteria

• Subject signed an informed consent.
• Subject is at least 18 years old.
• Subject has an acute, complicated Type B aortic dissection with evidence of at least one of the following:
• Malperfusion (visceral, renal, spinal cord and/or lower limb ischemia)
• Visceral ischemia measured by either radiographic or clinical evidence.
• Renal ischemia measured by either radiographic or clinical evidence.
• Spinal cord ischemia measured by either radiographic or clinical evidence.
• Lower limb ischemia measured by either radiographic or clinical evidence.
• Rupture - Measured by radiographic or clinical evidence.
• Subject is hemodynamically stable.
• Subject's anatomy must meet all of the following anatomical criteria:

Proximal landing zone aortic diameter must be between 20 mm and 44 mm;

• Centerline distance from distal margin of left CCA or in cases of bovine anatomy, innominate artery, to start of most proximal tear must be ≥ 20 mm;
• Subject has patent iliac or femoral arteries or can tolerate an iliac conduit that allows endovascular access to the dissection site with the delivery system of the appropriate sized device.
• Thoracic aortic dissection is confirmed, at a minimum, by diagnostic contrast-enhanced computerized tomography angiogram (CTA) with 3-D reconstruction, and/or contrast enhanced magnetic resonance angiogram (MRA) obtained prior to the implant procedure.

Exclusion Criteria

• Planned placement of the COVERED portion of the stent graft over the left carotid artery, or the celiac trunk.
• Subject has systemic infection.
• Subject is pregnant.
• Subject has received a previous stent or stent graft or previous surgical repair in the DTA.
• Subject has had a cerebral vascular accident (CVA) within 2 months.
• Subject has a history of bleeding diathesis, coagulopathy, or refuses blood transfusion.
• Subject has a history of Marfan Syndrome or other connective tissue disorder.
• Subject is currently participating in an investigational drug or device clinical trial which would interfere with the endpoints and follow-ups of this study.
• Subject has a known allergy or intolerance to the device components.
• Subject has a known hypersensitivity or contraindication to anticoagulants or contrast media, which is not amenable to pre-treatment.
• Subject has a co-morbidity causing expected survival to be less than 1 year.