1. A method, comprising the steps of: introducing a catheter into a coronary sinus of a heart of a living subject; while the catheter is in the coronary sinus acquiring a first set of frames comprising 2-dimensional images of the catheter; thereafter acquiring a second set of frames comprising 2-dimensional images of the catheter; establishing respective 2-dimensional models of the catheter in synchronized frames of the first set and the second set, the 2-dimensional models comprising respective tracked 2-dimensional paths of the catheter; synchronizing the first set with the second set by identifying frames of the first set and the second set that are in respective phases of a cardiorespiratory cycle; constructing first and second 3-dimensional models of the catheter from the synchronized frames; geometrically transforming the first and second 3-dimensional models to minimize a distance function therebetween; and displaying the transformed 3-dimensional models.