An apparatus, comprising: a cardiac catheter adapted for introduction into a coronary sinus of a heart of a living subject; a display; a fluoroscopic imaging device; and a processor, which is cooperative with the fluoroscopic imaging device and is configured for performing the steps of: importing image data of the heart obtained prior to introduction of the cardiac catheter; representing the image data as a first model of the heart in a first coordinate space, the first model comprising the coronary sinus; thereafter acquiring a first fluoroscopic image data of the cardiac catheter in the coronary sinus of the heart of the living subject; and then acquiring a second fluoroscopic image data of the cardiac catheter in the coronary sinus of the heart of the living subject, wherein the first and second fluoroscopic image data are acquired before and after a movement of the heart; wherein the first and second fluoroscopic image data are synchronised in a cardiorespiratory cycle of the living subject and the processor is further configured for performing the steps of: using the first and second fluoroscopic image data of the cardiac catheter to prepare a second model of the coronary sinus in a second coordinate space; and transforming the first model into the second coordinate space by placing the coronary sinus of the second model in registration with the coronary sinus of the first model. a cardiac catheter adapted for introduction into a coronary sinus of a heart of a living subject; a display; a fluoroscopic imaging device; and a processor, which is cooperative with the fluoroscopic imaging device and is configured for performing the steps of: importing image data of the heart obtained prior to introduction of the cardiac catheter; representing the image data as a first model of the heart in a first coordinate space, the first model comprising the coronary sinus; thereafter acquiring a first fluoroscopic image data of the cardiac catheter in the coronary sinus of the heart of the living subject; and then acquiring a second fluoroscopic image data of the cardiac catheter in the coronary sinus of the heart of the living subject, wherein the first and second fluoroscopic image data are acquired before and after a movement of the heart; wherein the first and second fluoroscopic image data are synchronised in a cardiorespiratory cycle of the living subject and the processor is further configured for performing the steps of: using the first and second fluoroscopic image data of the cardiac catheter to prepare a second model of the coronary sinus in a second coordinate space; and transforming the first model into the second coordinate space by placing the coronary sinus of the second model in registration with the coronary sinus of the first model. importing image data of the heart obtained prior to introduction of the cardiac catheter; representing the image data as a first model of the heart in a first coordinate space, the first model comprising the coronary sinus; thereafter acquiring a first fluoroscopic image data of the cardiac catheter in the coronary sinus of the heart of the living subject; and then acquiring a second fluoroscopic image data of the cardiac catheter in the coronary sinus of the heart of the living subject, wherein the first and second fluoroscopic image data are acquired before and after a movement of the heart; wherein the first and second fluoroscopic image data are synchronised in a cardiorespiratory cycle of the living subject and the processor is further configured for performing the steps of: using the first and second fluoroscopic image data of the cardiac catheter to prepare a second model of the coronary sinus in a second coordinate space; and transforming the first model into the second coordinate space by placing the coronary sinus of the second model in registration with the coronary sinus of the first model. using the first and second fluoroscopic image data of the cardiac catheter to prepare a second model of the coronary sinus in a second coordinate space; and transforming the first model into the second coordinate space by placing the coronary sinus of the second model in registration with the coronary sinus of the first model.