The purpose of this trial is to determine the safety and effectiveness of the Edwards SAPIEN XT transcatheter heart valve and delivery systems which are intended for use in patients with symptomatic, calcific, severe aortic stenosis.

The PIIA cohort is a prospective multi-center trial undergoing aortic valve replacement for severe aortic stenosis. Patients randomized to the treatment arm will receive an Edwards SAPIEN XT THV with either transfemoral, transapical or transaortic delivery access. Patients in the control arm will receive a surgical bioprosthetic heart valve via aortic valve replacement surgery.

To assure that patients with an STS score ≥ 4% have been selected.

Inclusion Criteria

1. Patient has senile degenerative aortic valve stenosis with echocardiographically derived criteria: mean gradient >40 mmHg or jet velocity greater than 4.0 m/s and an initial aortic valve area (AVA) of ≤0.8 cm2 or indexed EOA < 0.5 cm2/m2 Qualifying echo must be within 60 days of the date of the procedure.
2. Patient is symptomatic from his/her aortic valve stenosis, as demonstrated by NYHA Functional Class II or greater.
3. The heart team agrees (and verified in the case review process) that valve implantation will likely benefit the patient.
4. The study patient or the study patient'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 Institutional Review Board (IRB) of the respective clinical site.
5. The study patient agrees to comply with all required post-procedure follow-up visits including annual visits through 5 years and analysis close date visits, which will be conducted as a phone follow-up.
6. Study patient agrees to undergo surgical aortic valve replacement (SAVR) - if randomized to control treatment.

Exclusion Criteria

1. Evidence of an acute myocardial infarction ≤ 1 month (30 days) before the intended treatment [defined as: Q wave MI, or non-Q wave MI with total CK elevation of CK-MB ≥ twice normal in the presence of MB elevation and/or troponin level elevation (WHO definition)].
2. Aortic valve is a congenital unicuspid or congenital bicuspid valve, or is non-calcified.
3. Mixed aortic valve disease (aortic stenosis and aortic regurgitation with predominant aortic regurgitation >3+).
4. Preexisting mechanical or bioprosthetic valve in any position (except NR3).
5. Any therapeutic invasive cardiac procedure resulting in a permanent implant that is performed within 30 days of the index procedure (unless part of planned strategy for treatment of concomitant coronary artery disease). Implantation of a permanent pacemaker or ICD (S3 Cohort only) is not excluded.
6. Heart team assessment of inoperability (including examining cardiac surgeon).