A catheter sheath 10 includes an electrical lead 12 carrying a plurality of electrical conductors 16. A sleeve 20 is co-axially arranged about the electrical lead 12. At least one of a distal end of the lead 12 and a distal end of the sleeve 20 defines a plurality of displaceable petals 22, the petals 22 being displaceable between a first, inoperative position in which the petals 22 extend parallel to a longitudinal axis of the sleeve 20 and a second, operative position in which the petals 22 lie transversely to the longitudinal axis of the sleeve 20. At least one of the petals 20 carries at least one electrode 28, the, or each, electrode 28 being in electrical connection with a group of the conductors 16 of the lead 12.