Bleeding stomach ulcer. Gastroscope (endoscope) view of a bleeding gastric (peptic) ulcer of a 49 year-old male patient. This bleeding would normally be controlled by using an probe, which passes an electric current through the bleeding vessel to seal it (electrocautery). But this patient did not respond and required surgery. Ulcers are caused by excessive stomach acid (digestive juice). This acid, often combined with excess alcohol & caffeine, attacks the stomach wall, causing pain and discomfort. If the wall's protective mucus becomes thinned, possibly due to mental stress or bacterial attack, the acid can perforate the stomach wall.