A medical device adapted to be implanted in a vessel of a human body includes a housing that contains means for performing medical functions and an anchor for supporting the housing in an intended location and orientation within the vessel. The anchor is expandable from a low profile configuration adapted for delivery to an expanded configuration for engagement with the vessel wall. The anchor and delivery device are adapted to enable the medical device to be retrieved and repositioned or removed from the vessel. The anchor is adapted to apply sufficient force against the vessel wall to maintain the anchor in place but less force than that required to provide scaffolding support for the vessel.
