A catheter for radio frequent ablation of tissue which includes a flexible elongate member having proximal and distal extremities. The flexible elongate member is provided with a lumen in the distal extremity. A metal conducting electrode is secured to the distal extremity of the elongate member and has first and second extremities. The electrode is provided with a chamber therein which is in communication with the lumen. A conductor extends through the elongate member from the proximal to distal extremities for supplying radio frequency energy to the electrode. Coolant is disposed in the chamber and in contact with the electrode for dissipating heat created in the electrode by the application of radio frequency energy thereto. A sleeve made from an electrically insulating material extends over at least the first extremity of the electrode.