Before EHL, a dye is injected into your arm that makes the stone visible on an X-ray. You'll fast for a number of hours beforehand, and your doctor may tell you to stop taking certain medications. You’ll be put under anesthesia, and a flexible probe (ureteroscope) will be inserted into your urethra, near the stone. The probe delivers an electric current that creates shock waves, which break up the stone. The fragmented stone either passes through your bladder or is extracted by your doctor during EHL.