A delivery device for implanting a medical device that includes an expandable fixation member adapted to fix the position of the medical device within a lumen of a human body. The delivery device has an inner shaft rotatably disposed in a tubular outer shaft. A retention member is secured to and rotatable with the inner shaft and has a free end and a retainer portion adapted to protrude outwardly through an exit aperture in the outer shaft to extend circumferentially about the exterior of the outer shaft. The fixation member of the medical device may be retained on the tubular shaft in a low profile configuration by the outwardly protruding retainer portion and may be released to expand upon retraction of the retainer portion in response to rotation of the inner shaft.