A thermal ablation catheter includes an elongate body member having a heating element disposed over a predetermined length of its distal end. The heating element is suspended away from an exterior surface of the elongate member to form a circulation region thereunder. Thermally conductive fluid can be introduced through a lumen in the elongate member and distributed within the circulation region to improve heat transfer. The catheter is used to introduce the thermally conductive medium to a hollow body organ where the heating element raises the temperature of the medium sufficiently to induce injury to the lining of the organ. Optionally, an introducer sheath having an expandable cage at its distal end may be used in combination with a thermal ablation catheter. The expandable cage helps center the heating element on the catheter within the body organ and prevents direct contact between the heating element and the wall of the organ. Heat transfer and temperature uniformity can be enhanced by inducing an oscillatory flow of the heat transfer medium through the catheter while heat is being applied.