An implantable device for regulating blood flow through a blood vessel includes an elongated support. The support includes axially spaced apart first and second substantially annular support portions, and an x-shaped linking member linking the axially spaced apart portions to one another. The device also includes a valve membrane extending between the axially spaced apart support portions and having an upper portion, a lower portion and an intermediate portion. The valve membrane includes a first region and a second lower region. The first region is folded over the linking member for attachment and the second region is adjacent the first region and unattached to the linking member. The second region is movable between a first position to enable blood flow and a second position to inhibit blood flow.