Abstract: A guide wire (1) is provided which can be introduced intravascularly and which is used for implanting a catheter in a heart with an electrode (2, 5). In that arrangement, the guide wire (1) is first used as a temporary electrode (2, 5) for stimulating, defibrillating and/or sensing the heart in order to determine the optimum implantation position for the catheter to be introduced. When that optimum position is determined, the guide wire (1) is left at that position and the catheter is introduced along the guide wire (1) to the ascertained position and implanted. Once the catheter is implanted, the guide wire (1) is removed.