 A catheter is a very thin tube that is inserted into a vein in the patient’s leg and threaded to the heart where it delivers energy to treat the patient’s arrhythmia.In surgical procedures, a flexible probe is used directly on an exposed heart to apply the energy that interrupts the arrhythmia.By cooling the tip of a cryoablation catheter (cardiology) or probe (heart surgery) to sub-zero temperatures, the cells in the heart responsible for conducting the arrhythmia are altered so that they no longer conduct electrical impulses.