Methods and apparatus are provided for heating or cooling a patients whole body or a selected portion of a patients body. In one embodiment, the method begins by inserting a catheter having a dual balloon system into the large intestine of a patient. A heated or chilled liquid is conducted through a supply tube of the catheter and into the inner balloon. The liquid is evacuated from the inner balloon through a return lumen of the catheter. The outer balloon conducts heat transfer between the patients tissues and the inner balloon, and further provides a degree of safety against rupture of the inner balloon.
