Abstract: Medical devices for implantation in a body vessel are provided. A medical device according to the invention comprises a support structure and one or more graft members comprising a valve portion and a constraining portion. The support structure has a first, unexpanded configuration and a second, expanded configuration. The constraining portion is adapted to substantially prevent the support structure from achieving the second, expanded configuration. The valve portion is adapted to permit fluid flow through a body vessel in a first direction and substantially prevent fluid flow through the vessel in a second, opposite direction.