An instrument positionable with respect to a body valve in the body of a living subject for performing a predetermined procedure on the living subject at a predetermined location relative to the body valve. The instrument includes: a movement sensor for sensing movements of the body valve an effective portion for performing the predetermined procedure when the effective portion is at the predetermined location and an effective portion positioner for positioning the effective portion in the living subject. The effective portion is positionable using the effective portion positioner in response to the movements sensed by the movement sensor for positioning the effective portion at the predetermined location in order to perform the predetermined procedure.
