Cardiac ablation uses heat or cold energy to create tiny scars in the heart to block irregular electrical signals and restore the heart rhythm. One or more thin, flexible tubes (catheters) are inserted through an artery, usually in the groin, and guided to the heart. Sensors on the tip of the catheters apply the heat or cold energy. This illustration shows ablation catheters being applied near the pulmonary veins in a type of cardiac ablation called pulmonary vein isolation.