The electrode system includes a protective cover which is tubular in shape, which fits into the endoscope (40). A series of electrodes (2a - d) each comprising an electrically conducting membrane are connected by wires to cardio-version equipment. The conductive membrane is directly accessible from the outside of the cover. The system of ready-to-fit electrodes in intended to be used with an endoscope for effecting a cardio-version via the oesophageal tract. The system includes a protective cover which is tubular in shape, which fits into the endoscope (40) to cover the distal end of the endoscope. A series of electrodes (2a - d) each comprising an electrically conducting membrane are connected by wires whose free ends are connected to cardio-version equipment. Fixings are provided to attach the electrodes both to the distal end of the endoscope and to the tubular wall (31) of the cover. This ensures that the conductive membrane is directly accessible from the outside of the cover.
