The invention relates to a navigation assistance system for assisting in navigating an interventional instrument within a subject. An implanted object opening model (21) and a vessel opening model (27) are generated based on a provided interventional image data set, wherein the models define a respective position, shape and dimension in a frame of reference. These models and a position, which is also provided in the frame of reference, and optionally also a shape (25) of the interventional instrument are used for generating a graphical representation showing the implanted object opening model, the vessel opening model and the provided position and optionally shape of the interventional instrument, thereby providing guidance for a physician, which allows the physician to relatively easily navigate the interventional instrument such that it is moved through the opening of the implanted object and through the opening of the vessel.