A mapping and/or ablation catheter for introduction into a chamber having a wall accessible by a passage leading to the chamber. The catheter includes a flexible elongate member extending along a longitudinal axis and having a distal extremity. An elongate flexible element is provided and has one end secured to the distal extremity of the flexible elongate member and an opposite free end. The elongate flexible element is movable between a first position in which it is adaptable to conform generally to the contour of the passage and a second position in which it has a coil-like configuration. The elongate flexible element serves to form at least one electrode. The elongate flexible element is passed through the passage into the chamber when in the first position and the at least one electrode is moved into engagement with the wall for mapping and/or ablating of the wall when the elongate flexible element is in the second position.