Nitinol Circular Blade

Inclusion Criteria: * Severe aortic stenosis defined as one or more of the following by Doppler echocardiography: mean gradient \>40 mmHg; max velocity \>4 m/sec; aortic valve area \<=0.8 cm2. * Symptoms related to aortic valve disease, and NYHA Functional Class II or greater * Subject is indicated for aortic valve implantation with a biological prosthesis (tissue valve) * Age \>= 65 years * Echocardiographically determined aortic annulus diameter \>=24 mm and \<=30 mm in a long-axis view * Subject understands the implications of participating in the study and provides informed consent Exclusion Criteria: * Congenital unicuspid aortic valve * Severe eccentricity of calcification, defined as calcium deposits larger than 6 mm in diameter * Echocardiographic evidence of intracardiac mass, thrombus or vegetation * Left ventricular ejection fraction \<25% as determined by contrast ventriculography, or echocardiography or radionuclide angiography if contrast ventriculography not available * Hypertrophic obstructive cardiomyopathy * Subjects with life expectancy less than 12 months due to an underlying non-cardiac co-morbid disease * Known hypersensitivity or contraindication that cannot be adequately controlled with pre-medication to any study medication or material, such as contrast medium or Nitinol * Blood dyscrasia such as acute anemia, leucopenia, or thrombocytopenia; bleeding diathesis, or coagulopathy * Renal insufficiency assessed by creatinine \>2.5 mg/dl and/or end stage renal disease requiring chronic dialysis * Poor lung function that in the investigator's opinion is prohibitive for thoracotomy * Active peptic ulcer or GI bleeding within 3 months from the planned index procedure * Cardiogenic shock, suspected cardiogenic shock, or hemodynamic instability requiring inotropic support or mechanical heart assistance * Peripheral vascular disease, including abdominal and thoracic aortic disease, that could pose a problem for eventual transarterial mechanical support (e.g. intraaortic balloon pump) * History of myocardial infarction in the last 6 weeks * History of TIA or CVA in the last 6 months * Subject refuses to have a blood transfusion * Subject is currently enrolled in another investigational device or drug trial that may influence the outcome of this trial