What happens when a bleeding ulcer is left untreated?

Not a good idea.: Ulcers that bleed have eroded into a blood vessel. Small blood vessel may spontaneously stop bleeding, while larger ones may require endoscopy or surgery. Even when the bleeding stops by itself, the ulcer should be treated to prevent further bleeding or perforation. Medications can be very effective. The first step is to contact your doctor or a gastroenterologist for a history, physical and test.