Haematemesis is the vomiting of blood. This condition occurs when there is bleeding in the oesophagus, stomach or duodenum, i.e. bleeding proximal to the duodenal-jejunal junction. It is very rare for bleeding entering the gut distal to this point to return to the stomach.
The colour and volume of the vomitus is an indicator to how long the blood has been in the stomach. Dark blood or 'coffee grounds' suggests a smaller bleed which has been altered by contact with gastric acid. A large volume of bright red blood is suggestive of a rapid and sizeable haemorrhage.