The clinical investigation is a multi-center, multi-country, prospective, non-randomized, observational study without concurrent or matched controls, designed to evaluate the safety and effectiveness of the Trifecta valve. A maximum of 120 subjects requiring aortic valve replacement will be implanted at a maximum of 6 investigational sites in Europe. The sample size is based on late patient-years of follow-up with a minimum of 400 late patient-years experience required.