surgeon to place sutures around the sewing ring more accurately by placing a suture at each of the marks rather that estimating the placement of the sutures as was done in the past the invention may also be used with other types of heart valves a flexible leaflet valve 30 is illustrated for example in fig3 and fig4 the flexible leaflet valve 30 comprises a valve body 32 with a plurality of commissure supports 34 36 38 surrounding a central orifice flexible leaflets 40 42 44 connected between adjacent commissure supports open and close to permit and resist the flow of blood through the valve 30 the leaflets are illustrated in a closed position the leaflets may be comprised of treated tissue such as bovine or porcine pericardium or of an artificial material such as an elastomeric polymer the flexible leaflet valve 30 may also have a supporting stent not shown as is known in the art a circumferential sewing ring 46 surrounds the valve body 32 and is connected to the valve body six marks 48 a 48 b 48 c 48 d 48 e and 48 f are provided circumferentially on the sewing ring as explained above these marks may be symmetrically spaced around the ring.