Inclusion Criteria:  Subject must provide written informed consent prior to any clinical investigation-related procedure. Are >60 years of age in host country, have severe symptomatic (NYHA class ≥ II) aortic stenosis (AS), at high or extreme surgical risk and have been identified as a candidate for a Portico valve implant. Subjects must have a Society of Thoracic Surgeons (STS) score of ≥7% OR documented heart team agreement of high or extreme risk for surgical aortic valve replacement due to frailty or co-morbidities not captured by the STS score.  Exclusion Criteria:  Have tested positive for the Corona Virus Disease 2019 (COVID-19) virus at any time AND currently have residual signs or symptoms associated with the COVID-19 virus (eg. evidence of thrombosis, damaged/inflamed heart muscle, damaged/inflamed lung tissue, etc.) Have sepsis, including active endocarditis Have any evidence of left ventricular or atrial thrombus Have vascular conditions (i.e. caliber, stenosis, tortuosity, or severe calcification) that make insertion and endovascular access to the aortic valve improbable Have a non-calcified aortic annulus Have congenital bicuspid or unicuspid leaflet configuration Are unable to tolerate antiplatelet/anticoagulant therapy Are pregnant at the time of signing informed consent Are currently participating in a drug or device study that may impact this study (unless prior sponsor approval for co-enrollment is granted)