This investigation is a prospective, non-randomized, multi-center trial of the PERCEVAL valve implanted in patients requiring aortic valve replacement. The study will be conducted in a maximum of 25 centers in the United States. Patients will be evaluated at each of the following time intervals:preoperative, at implant, in the early postoperative period, in the late postoperative period (between 3 and 6 months postoperatively), at 1 year (between 11 and 13 months postoperatively), and annually until study completion. The duration of the study is anticipated to be 5 years.