input into machine tooling which cuts an electrode into the corresponding shape finally the electrode is used to dissolve a pattern into a block of a suitable metal such as a nickel steel alloy into the final mold for injection molding the stents the basic geometry of the inner stent 3 is determined by three parameters dependent on the size and strength of the valve desired namely the post width the scallop height above the base and the inner diameter of the valve the post width is determined from the strength desired for the inner stent and the requirement that the completed valve fully close the post must be made wide enough to give the inner stent sufficient strength but must not be made so wide that the amount of tissue draped over the inner stent posts is so great that the valve cannot properly close representative values for this dimension which have been found acceptable in practice for variously sized valves are given in column k in table 1 the scallop height must be sufficient to achieve three objectives 1 allow the leaflets of the valve to completely close 2 provide sufficient flexibility to absorb the shock of valve closure and 3 distribute the stresses encountered during normal use of the valve evenly throughout the tissue leaflet area the choice of the inner diameter of the valve is based on the size of the patient 39 s annulus as measured during the surgical procedure with an obturator such as that disclosed in the present assignee 39 s pending application ser no 08.