Gastric varicose veins. Gastroscope (endoscope) view of widened (varicose) veins in the stomach due to portal hypertension (high blood pressure). Gastric varices occur when liver damage causes high blood pressure in the portal vein, which takes blood from the spleen, stomach and intestines to the liver. This causes the veins in the stomach to widen. The veins may rupture, causing bouts of vomiting blood and black faeces. Surgery to reduce the pressure in the portal vein may effect a cure, or the veins can be injected with a sclerosant, which permanently clots them.