Possible causes for a dog to throw up blood, called hematemisis, could be irritation of the intestines and a disruption of the dog's esophagus, explains PetMD. Dogs may also vomit blood they swallowed due to mouth injuries. Dogs that are critically ill possess a higher risk of hematemisis.
If a dog is vomiting blood, the owner should consult with a veterinarian as soon as possible, advises Banfield Pet Hospital. The bleeding could be from intestinal tract bleeding, which is life-threatening. A dog that loses an excessive amount of blood may have complications with his internal organs. Trauma, ingestion of foreign substances, stomach ulcers or kidney disorders are also cause for bloody vomit in dogs.