An apparatus, comprising: a cardiac catheter adapted for introduction into a coronary sinus of a heart of a living subject; a display (49, 29); a fluoroscopic imaging device (37, 169) and a processor, which is cooperative with the fluoroscopic imaging device (37, 169) for performing the steps of: while the catheter is in the coronary sinus activating the fluoroscopic imaging device (37, 169) to acquire a first set of frames comprising 2-dimensional images of the catheter and thereafter acquiring a second set of frames comprising 2-dimensional images of the catheter, wherein the fluoroscopic imaging device (37, 169) acquires the first set and the second set at a first primary angle and at a second primary angle and wherein the first primary angle and the second primary angle are defined relative to a sagittal plane of the subject and the difference between the first and second primary angles is not more than 120 degrees; establishing respective 2-dimensional models of the catheter in 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 a first pair of frames from the first set and the second set at the first primary angle and a second pair of frames from the first set and the second set at the second primary angle that are in respective phases of a cardiorespiratory cycle; constructing first and second 3-dimensional models of the catheter from the synchronized frames, wherein constructing the 3-dimensional models comprises searching for a 3-dimensional model whose projections on the images are as close as possible to the tracked 2-dimensional paths; geometrically transforming the first and second 3-dimensional models to minimize a distance function therebetween; and displaying the transformed 3-dimensional models on the display (49, 29). a cardiac catheter adapted for introduction into a coronary sinus of a heart of a living subject; a display (49, 29); a fluoroscopic imaging device (37, 169) and a processor, which is cooperative with the fluoroscopic imaging device (37, 169) for performing the steps of: while the catheter is in the coronary sinus activating the fluoroscopic imaging device (37, 169) to acquire a first set of frames comprising 2-dimensional images of the catheter and thereafter acquiring a second set of frames comprising 2-dimensional images of the catheter, wherein the fluoroscopic imaging device (37, 169) acquires the first set and the second set at a first primary angle and at a second primary angle and wherein the first primary angle and the second primary angle are defined relative to a sagittal plane of the subject and the difference between the first and second primary angles is not more than 120 degrees; establishing respective 2-dimensional models of the catheter in 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 a first pair of frames from the first set and the second set at the first primary angle and a second pair of frames from the first set and the second set at the second primary angle that are in respective phases of a cardiorespiratory cycle; constructing first and second 3-dimensional models of the catheter from the synchronized frames, wherein constructing the 3-dimensional models comprises searching for a 3-dimensional model whose projections on the images are as close as possible to the tracked 2-dimensional paths; geometrically transforming the first and second 3-dimensional models to minimize a distance function therebetween; and displaying the transformed 3-dimensional models on the display (49, 29). while the catheter is in the coronary sinus activating the fluoroscopic imaging device (37, 169) to acquire a first set of frames comprising 2-dimensional images of the catheter and thereafter acquiring a second set of frames comprising 2-dimensional images of the catheter, wherein the fluoroscopic imaging device (37, 169) acquires the first set and the second set at a first primary angle and at a second primary angle and wherein the first primary angle and the second primary angle are defined relative to a sagittal plane of the subject and the difference between the first and second primary angles is not more than 120 degrees; establishing respective 2-dimensional models of the catheter in 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 a first pair of frames from the first set and the second set at the first primary angle and a second pair of frames from the first set and the second set at the second primary angle that are in respective phases of a cardiorespiratory cycle; constructing first and second 3-dimensional models of the catheter from the synchronized frames, wherein constructing the 3-dimensional models comprises searching for a 3-dimensional model whose projections on the images are as close as possible to the tracked 2-dimensional paths; geometrically transforming the first and second 3-dimensional models to minimize a distance function therebetween; and displaying the transformed 3-dimensional models on the display (49, 29).