Study Summary: This study is researching the safety and how well the SAPIEN X4 Transcatheter Heart Valve (THV) works in people with severe aortic stenosis (AS). Aortic stenosis is when the aortic valve in the heart becomes too narrow, making it hard for blood to flow. The study is "prospective," meaning it looks forward to see how things turn out for participants.

Eligibility: To join, you must have severe AS and a heart that can fit the SAPIEN X4 THV. You also need to be at least at NYHA class II, which means you feel some symptoms during normal activity. NYHA is a way doctors classify heart failure. You cannot join if you have certain heart issues or other health conditions like severe aortic or mitral valve problems, or if you've had a heart attack recently.

• The study is single-arm, meaning everyone gets the same treatment.
• It takes place at multiple locations (multicenter).
• You will need to give written consent to join.