1. A method for determining by an x-ray projection a position of a target radiopaque marker disposed on a catheter in a subject's body, comprising: assigning a landmark in the body as a reference point compensated for periodic movements of the body; determining an auxiliary location relative to the reference point using at least one additional radiopaque marker disposed on the catheter; and based on the auxiliary location determining the position of the target radiopaque marker with respect to the reference point.