1. A method for 3D reconstruction of the positions of a catheter as it is moved within a region of a human body, comprising: (a) ascertaining the 3D position of a point on a catheter for insertion into the body region; (b) acquiring a fixed angle, single-plane fluoroscopic image of the body region and of the catheter; (c) transferring the image data and catheter-point position to a computer; (d) determining the 2D image coordinates of the point on the catheter; (e) changing the length of catheter insertion by a measured amount; (f) thereafter acquiring a further single-plane fluoroscopic image of the body region and the catheter from the same angle, transferring the length change and additional image data to the computer, and determining the 2D image coordinates of the point on the catheter; (g) computing the 3D position of the catheter point; and (h) repeating steps e-g plural times.