This randomized controlled double-blind intervention study unravels influence of dietary plant sterols and stanols on the structure and the sterol composition of the human aortic valve. The study patients will include 50-60 voluntary patients from the Helsinki Univ. Central Hospital, who will undergo aortic valve surgery. The patients will be randomized into plant sterol (E), plant stanol (A) and control (C) groups. Patients in the E and A groups will be asked to consume daily 2 grams plant sterols or plant stanols, respectively, in a margarine product.