Safety and Efficacy Study of the Medtronic CoreValve® System in the Treatment of Severe, Symptomatic Aortic Stenosis in Intermediate Risk Subjects Who Need Aortic Valve Replacement (SURTAVI).

The purpose of the study is to investigate the safety and efficacy of transcatheter aortic valve implantation (TAVI) in patients with severe, symptomatic Aortic Stenosis (AS) at intermediate surgical risk by randomizing patients to either Surgical Aortic Valve Replacement (SAVR) or TAVI with the Medtronic CoreValve® System. Single Arm: The purpose of this trial is to evaluate the safety and effectiveness of transcatheter aortic valve implementation (TAVI) in patients with severe symptomatic Aortic Stenosis (AS) at intermediate surgical risk with TAVI. This is a non-randomized phase of the pivotal clinical trial.

Inclusion Criteria: * Subject must have co-morbidities such that Heart Team agrees predicted risk of operative mortality is ≥3% and \ 40mmHg or Vmax \> 4m/sec by resting echocardiogram or simultaneous pressure recordings at cardiac catherization \[or with dobutamine stress, if subject has left ventricular ejection fraction (LVEF) \