Inclusion Criteria:

Native Aortic Stenosis Cohorts:

1. The subject is a candidate for TAVR using the DurAVR® THV System, and a SAPIEN series THV system or an Evolut series THV System.
2. The local Heart Team agrees that the subject has an appropriate indication for, and will benefit from, TAVR due to native calcific valve severe aortic stenosis.
3. Subject understands the study requirements and the treatment procedure and provides written informed consent.

ViV Registry Cohort:

1. Severe degeneration of a surgically implanted aortic bioprosthetic valve.
2. Subject requires aortic valve replacement and is high surgical risk and is indicated for TAVR Valve-in-Valve procedure as determined by the Heart Team.
3. Subject understands the study requirements and the treatment procedure and provides written informed consent.

Exclusion Criteria:

Native Aortic Stenosis Cohorts:

1. Native aortic annulus size unsuitable for study THVs (investigational or control) based on CT imaging analysis.
2. Access vessel characteristics that would preclude safe placement of the introducer sheath (investigational or control).
3. Evidence of an acute myocardial infarction 30 days before randomization.
4. AV is unicuspid, Type 0 bicuspid, or is non-calcified.
5. Severe total aortic regurgitation
6. Severe mitral or tricuspid regurgitation or ≥ moderate mitral stenosis.
7. Pre-existing mechanical or bioprosthetic valve in any position.
8. Untreated clinically significant coronary artery disease (CAD) requiring revascularization.
9. Cardiac imaging evidence of intracardiac mass, thrombus, or vegetation.
10. Active bacterial endocarditis in the last 3 months.
11. Estimated life expectancy (after TAVR) <12 months.
12. Subject is not a candidate for both arms (investigational and control) of the study.
13. Subject belongs to a vulnerable population

ViV Registry Cohort:

1. Anatomy precluding safe placement of DurAVR THV.
2. Pre-existing prosthetic heart valve in the mitral, tricuspid or pulmonary position.
3. Severe mitral or tricuspid regurgitation or ≥ moderate mitral stenosis
4. Cardiac imaging evidence of intracardiac mass, thrombus or vegetation.
5. Failing surgical aortic bioprosthesis is unstable, rocking, or not structurally intact.
6. Evidence of an acute myocardial infarction ≤ 30 days before the intended treatment.
7. Untreated clinically significant coronary artery disease (CAD) requiring revascularization.
8. Need for emergency surgery for any reason
9. GI bleeding within the past 3 months.
10. Active bacterial endocarditis in the last 3 months.
11. Estimated life expectancy (after TAVR) <12 months.
12. Subject belongs to a vulnerable population.