prosthesis 150 that prevents the flow of blood through the lumen 156 the graft material 165 extends around the inner circumference of the annular support members 161 so that graft material 165 and the support structure 161 when in the closed position form a leak resistant seal with the inner wall of the short iliac portion 154 in addition to attaching the graft 165 to the inner wall of the short iliac portion 154 the valve 160 is held in position within the short iliac portion 154 by the radial force of the support member 161 which may be a spring member formed e g of nitinol the support member 161 holds the valve 160 in the first and closed position in fig1 and 13 and in the second and open position in fig1 and 15 the support member 161 may be flipped from a first position in which the valve 160 is closed to a second position in which the valve 160 is open in the first position the support member forms a semicircle with an inner and outer circumference when it is in its second position the side forming the inner circumference in the first position becomes the outer circumference in the second position and the side forming the outer circumference in the first position becomes the inner circumference in the second position when the support member 161 is flipped over into the second open position as illustrated in fig1 and 15 the graft material 165 surrounding the support member 161 that in the first position formed the cover 167 and the graft material 165 that is attached to the inner wall of the short iliac portion 154 is held.