ALLIANCE: Safety and Effectiveness of the SAPIEN X4 Transcatheter Heart Valve

Inclusion Criteria: 1. Severe, calcific AS 2. Native aortic annulus size suitable for SAPIEN X4 THV 3. NYHA functional class ≥ II 4. The subject has been informed of the nature of the study, agrees to its provisions and has provided written informed consent. Exclusion Criteria: 1. Anatomical characteristics that would preclude safe femoral placement of the introducer sheath or safe passage of the delivery system 2. Aortic valve is unicuspid, bicuspid or non-calcified 3. Pre-existing mechanical or bioprosthetic valve in any position 4. Severe aortic regurgitation (\> 3+) 5. Severe mitral regurgitation (\> 3+) or ≥ moderate mitral stenosis 6. Need for mitral, tricuspid or pulmonic valve intervention within the next 12 months 7. Left ventricular ejection fraction \< 20% 8. Cardiac imaging evidence of intracardiac mass, thrombus or vegetation 9. Left ventricular outflow tract calcification that would increase the risk of annular rupture or significant PVL after THV implantation 10. Increased risk of coronary artery obstruction after THV implantation 11. Myocardial infarction within 30 days prior to the study procedure 12. Hypertrophic cardiomyopathy with subvalvular obstruction 13. Subjects with planned concomitant ablation for atrial fibrillation 14. Complex coronary artery disease (CAD) that cannot be optimally treated by percutaneous coronary intervention (PCI) 15. Any surgical or transcatheter procedure within 30 days prior to the study procedure (unless part of planned strategy for treatment of CAD). Implantation of a permanent pacemaker or implantable cardioverter defibrillator (ICD) is not considered an exclusion. 16. Any planned surgical or transcatheter intervention to be performed within 30 days following the study procedure (unless part of planned strategy for treatment of CAD) 17. Endocarditis within 180 days prior to the study procedure 18. Stroke, transient ischemic attack or neurological signs and symptoms attributed to carotid or vertebrobasilar disease within 90 days prior to the study procedure 19. Hemodynamic or respiratory instability requiring inotropic or mechanical support within 30 days prior to the study procedure 20. Renal insufficiency and/or renal replacement therapy 21. Leukopenia, anemia, thrombocytopenia 22. Inability to tolerate or condition precluding treatment with antithrombotic therapy 23. Hypercoagulable state or other condition that increases risk of thrombosis 24. Absolute contraindications or allergy to iodinated contrast that cannot be adequately treated with premedication 25. Subject refuses blood products 26. BMI \> 50 kg/m2 27. Estimated life expectancy \< 24 months 28. Female who is pregnant or lactating 29. Active SARS-CoV-2 infection or previously diagnosed with COVID-19 with sequelae that could confound endpoint assessments 30. Participating in another investigational drug or device study that has not reached its primary endpoint 31. Subject considered to be part of a vulnerable population