Hematemesis is also clinically known as gastrointestinal bleeding, which includes upper and lower gastrointestinal bleeding. For upper gastrointestinal bleeding common causes include gastric ulcer, duodenal bulb ulcer, gastric cancer, and erosive gastritis, all of which can result in large mouthfuls of blood, while lower gastrointestinal bleeding is mainly seen in intestinal cancer, hemorrhoids, or ulcerative colitis. For gastrointestinal bleeding, gastroscopy, colonoscopy or small intestine microscopy should be improved to clarify the diagnosis, and different treatment plans should be taken according to the different causes. If there is a large mouthful of blood, it is recommended to go to the hospital for treatment in time to avoid delay. Also, the head should be tilted to the side when vomiting blood to prevent suffocation.