Inclusion Criteria Cohort A

1. Patients must have co-morbidities such that the surgeon and cardiologist Co-PIs concur that the predicted risk of operative mortality is ≥15% and/or a minimum STS score of 10
2. Patient has senile degenerative aortic valve stenosis with echocardiographically derived criteria: mean gradient >40 mmHg or jet velocity greater than 4.0 m/s or an initial aortic valve area of < 0.8 cm2
3. Patient is symptomatic from his/her aortic valve stenosis, as demonstrated by NYHA Functional Class II or greater
4. The subject or the subject's legal representative has been informed of the nature of the study, agrees to its provisions and has provided written informed consent as approved by the IRB of the respective clinical site

5. The subject and the treating physician agree that the subject will return for all required post-procedure follow-up visits

   Cohort B All candidates for Cohort B of this study must meet #2, 3, 4, 5 of the above criteria and

6. The subject, after formal consults by a cardiologist and two cardiovascular surgeons agree that medical factors preclude operation, based on a conclusion that the probability of death or serious, irreversible morbidity exceeds the probability of meaningful improvement. Specifically, the probability of death or serious, irreversible morbidity should exceed 50%.

Exclusion Criteria

1. Evidence of an acute myocardial infarction ≤ 1month before the intended treatment
2. Aortic valve is a congenital unicuspid or bicuspid valve; or is non-calcified
3. Mixed aortic valve disease (aortic stenosis and aortic regurgitation with predominant aortic regurgitation >3+)
4. Any therapeutic invasive cardiac procedure performed within 30 days of the index procedure, (or 6 months if the procedure was a drug eluting coronary stent implantation)
5. Pre-existing prosthetic heart valve in any position, prosthetic ring, or severe (greater than 3+) mitral insufficiency
6. Blood dyscrasias as defined: Leukopenia, acute anemia, thrombocytopenia, history of bleeding diathesis or coagulopathy
7. Untreated clinically significant coronary artery disease requiring revascularization
8. Hemodynamic instability requiring inotropic support or mechanical heart assistance.
9. Need for emergency surgery for any reason
10. Hypertrophic cardiomyopathy with or without obstruction
11. Severe ventricular dysfunction with LVEF <20
12. Echocardiographic evidence of intracardiac mass, thrombus or vegetation
13. Active peptic ulcer or upper GI bleeding within the prior 3 months
14. A known hypersensitivity or contraindication to aspirin, heparin, ticlopidine, or clopidogrel, or sensitivity to contrast media, which cannot be adequately pre-medicated
15. Native aortic annulus size < 16mm or > 24mm per the baseline echo as estimated by the LVOT
16. Patient has been offered surgery but has refused surgery.
17. Recent (within 6 months) CVA or a TIA
18. Renal insufficiency and/or end stage renal disease requiring chronic dialysis
19. Life expectancy < 12 months due to non-cardiac co-morbid conditions.
20. Significant aortic disease, including abdominal aortic or thoracic aneurysm defined as maximal luminal diameter 5cm or greater; marked tortuosity (hyperacute bend), aortic arch atheroma or narrowing (especially with calcification and surface irregularities) of the abdominal or thoracic aorta, severe "unfolding" and tortuosity of the thoracic aorta(applicable for transfemoral patients only).
21. Iliofemoral vessel characteristics that would preclude safe placement of 22F or 24F introducer sheath such as severe obstructive calcification, severe tortuosity or vessels size less than 7 mm in diameter(applicable for transfemoral patients only).
22. Currently participating in an investigational drug or another device study