A system includes a medical device for implanting in a valve of a subject, the implantable medical device having a self-expanding frame； and a holder configured to retain the frame of the implantable medical device in a constricted configuration and to control expansion of the frame. The holder has a controllably constrictable and expandable loop, wherein the loop is disposed about at least a portion of the self-expanding frame such that constriction or expansion of the first loop controls constriction or expansion of the frame.
