A system for determining the proximity of the esophagus to the ablation electrode of an ablation catheter during an ablation procedure is disclosed. The system comprises an ablation catheter having at least one ablation electrode, an esophageal probe catheter having at least one electrode, and a signal processing unit. Both the ablation electrode and the esophageal probe catheter are electrically connected to the signal processing unit. The signal processing unit receives electrical signals from the ablation electrode on the ablation catheter and the electrode on the esophageal probe catheter and compares the signals to determine the proximity of the esophagus to the ablation electrode.