A flexible non-stented heart valve prosthesis made from a flat piece of a stabilized biological membrane. The membrane is folded along one or more folding lines and attached to a flat flexible non-biological base material so that one or more leaflets are formed. Preferably the membrane is pericardium and is attached by machine stitching to a woven polymeric base material. Different valve types including ventricular outflow patches and three-leaflet valves such as aortic valves and methods for their production are described.
The aortic valve is preferably made from three separate leaflets provided with narrow base materials serving as attachment margins which are stitched together in a manner to form a three-leaflet valve.