gastric dilitation and volvulus, or "bloat". When stomach twists, cutting off esophagus and duodenum. Stomach keeps digesting, fills with air, expands. Symptoms: gagging, heaving, breathing heavily, pain when you touch the abdomen. Common in deep-chested or large-breed dogs (great dane, g. shep, retrievers. Looks like the popeye sign on a radiograph. Treated by fixation.