An occlusion device includes a braiding of thin wires or threads tapering to the diameter of a catheter used for an intravascular implantation/explantation procedure and having a proximal retention area, a distal retention area at which ends of the wires or threads converge into a holder, and a cylindrical crosspiece interposed between the proximal retention area and the distal retention area, whereby the two retention areas are positioned on two sides of a shunt to be occluded in a septum following implantation while the crosspiece transverses the shunt. The holder exhibits a head section at its free end having an eyelet as a cross-hole which can be gripped and held in form-fit fashion by an implantation/explantation instrument. A surgical instrument having such a holder includes gripper tongs with gripping jaws which open and close by a push/pull system, and which force-fit grips the head section of the holder.