An improved device for use in a conduit, such as a blood vessel, is provided. The device uniquely combines desirable properties from two distinct previous devices. The device of the present invention assumes and is constrained to a first diametrical dimension for insertion into the conduit. Once inserted and properly positioned in the conduit the device expands to a second diametrical dimension within the conduit when the constraint is removed. The device can then be dilated to one or more enlarged third diametrical dimensions by using a balloon catheter or similar device. The result is a device that provides desirable properties of both self-expanding stents and balloon-expandable endoprostheses. The device can be employed in a variety of applications.