Using a catheter, a cardiologist with expertise in the heart's electrical system (electrophysiologist) positions a probe inside the heart. Radio-frequency energy or cold is used to isolate the areas triggering the arrhythmia. Since A-fib commonly originates in the pulmonary veins, which drain blood from the lungs into the left atrium, these veins are targeted. Cleveland Clinic electrophysiologists also ablate the back wall of the left atrium. The technique creates areas of therapeutic scar tissue that lower the risk of transmitting irregular electrical signals.