1. A method for tracking a surgical device in a body organ of a subject during a surgical procedure, wherein the body organ is a non-rigid body organ that changes shape as a result of varying patient body posture or position thereby defining an anatomy of unknown shape, the body organ comprising at least one body lumen, and said surgical device comprising a distal section having at least one reference mark which is visible under fluoroscopy, the method comprising the steps of: a) receiving a 3D image data set of the body organ and computing a 3D model of the body organ; b) performing a pre-tracking registration prior to tracking the surgical device during the surgical procedure thereby registering an image derived from the 3D model of the body organ with a real-time fluoroscopy image; wherein the pre-tracking registration comprises the following steps: receiving a pre-tracking position from a sensor indicating the position of a fluoroscopy unit; receiving a pre-tracking fluoroscopy image corresponding to the pre-tracking position; registering the pre-tracking fluoroscopy image with a pre-tracking image derived from the 3D model of the body organ; and recording the pre-tracking position; c) advancing the distal section of the surgical device outside of the at least one body lumen and into the anatomy of unknown shape; d) receiving a real-time fluoroscopy image showing the reference mark of the surgical device outside of the at least one body lumen and in the anatomy of unknown shape; and e) computing a 3D location of the surgical device in the 3D model based on a shape or pattern of the reference mark outside the at least one body lumen and within the anatomy of unknown shape and visible in the fluoroscopy image of step ( d ).