NVT ALLEGRA TAVI System TF in Failing Calcified Aortic Heart Valves in a Real-world Patient Population

Inclusion Criteria: 1. Symptomatic degeneration of severe calcified aortic heart valve OR failing surgical aortic bioprosthetic valve 2. Acceptable candidate for elective treatment with the ALLEGRA TAVI System TF (according to the most recent version of the ALLEGRA Instructions For Use) 3. High risk for surgery as assessed by the heart team 4. Has signed the Patient Informed Consent Form \>= 18 years Exclusion Criteria: General: 1. Echocardiographic evidence of intracardiac thrombus or vegetation 2. Significant aortic disease such as severe obstructive calcification or marked tortuosity or kinking which will preclude a safe advancement of the ALLEGRA TAVI System TF 3. Iliofemoral vessel conditions such as severe obstructive calcification, severe tortuosity or kinking that would preclude safe placement of an 18 Fr introducer sheath or make endovascular access to the aortic valve impossible 4. Severe ventricular dysfunction with LVEF \<20% 5. Evidence of active endocarditis or other acute infections 6. Renal failure requiring continuous renal replacement therapy 7. Known hypersensitivity to contrast media, which cannot be adequately pre-medicated or contraindication to anticoagulant or anti-platelet medication or to nitinol alloy or to bovine tissue 8. Life expectancy ≤ 12 months due to other medical illness 9. Currently participating in another investigational drug or device study Patients with native aortic valve disease: 1. Unicuspid or bicuspid aortic valve 2. Non-calcified aortic stenosis 3. Combined aortic valve disease with predominant aortic regurgitation \> 3 4. Distance between aortic valve basal plane and the orifice of the lowest coronary artery \< 8 mm Patients with degenerated surgical bioprosthetic aortic valves: 1. Low position of the coronary ostia, especially in combination with shallow sinuses 2. Internal diameter of the bioprosthesis is ≤16 mm or \>28 mm 3. Partially detached leaflets that in the aortic position may obstruct a coronary ostium