A medical device for treating a heart valve insufficiency, with an endoprosthesis which can be introduced into a patient's body and expanded to secure a heart valve prosthesis in the patient's aorta with a catheter. In an embodiment, the endoprosthesis has a plurality of positioning arches configured to be positioned with respect to a patient's aorta and a plurality of retaining arches to support a heart valve prosthesis. The endoprosthesis includes a collapsed mode during the process of introducing it into the patient's body and an expanded mode when it is implanted. The endoprosthesis may be introduced into a patient's body and expanded via a catheter. In an embodiment, the catheter has first and second slide mechanisms configured to independently manipulate first and second sleeve elements to sequentially expand the endoprosthesis from the collapsed mode to the expanded mode.