Abstract: A heat exchange balloon assembly (11) for cooling the esophagus during heat ablation treatment to the heart is disclosed. The heat exchange balloon assembly includes an inflatable balloon (4) adapted for insertion into the esophagus, provided with an exterior heat-transfer surface and a lumen within the inflatable balloon (4) adapted to carry thermal exchange medium configured such that said heat-transfer surface conducts thermal energy between the esophagus and the lumen. Also disclosed is a heat exchange balloon assembly (11) connected to a temperature controller provided with a means to receive data pertinent to the power supplied to an ablation probe and/or the temperature of the tip of the ablation probe. The device may be used in an ablation system and in a method for treatment of atrial fibrillation.