The Valiant Mona LSA thoracic stent graft system is for the endovascular repair of aneurysms of the descending thoracic aorta (DTA) in patients who require coverage of the left subclavian artery (LSA).The study is intended to assess safety and performance of the device acutely and at 30 days.

Inclusion Criteria:

• Subject is at least 18 years of age.
• The subject or legal guardian understands the nature of the study and agrees to its provisions on a written informed consent form
• Subject must be considered a candidate for revascularization of the LSA.
• Subject has a DTA which will require coverage of the LSA
• Subject's anatomy must meet the anatomical criteria to receive that implanted device

Exclusion Criteria:

• Subject has had previous endovascular repair of the ascending and/or descending thoracic aorta.
• Subject is in acute renal failure or has renal insufficiency with a serum creatinine ≥ 2.0 mg/dL
• Subject is a pregnant female.
• Enrollment in another clinical study
• Subject has had a cerebral vascular accident (CVA)or myocardial infarction (MI) within 3 months.
• Subject has a history of bleeding diathesis, coagulopathy, or refuses blood transfusion.
• 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.

Through 30 days

Investigators are required to assess for adverse events at each follow-up timepoint, including discharge, 30 days, 6 months, 12 months, 24 months, 36 months, 48 months, and 60 months. Per protocol, all adverse events are required to be reported, regardless of relationship.