A hiatal hernia is what doctors call it when a partof the stomach moves up into the chest area. Normally, the stomach sits below the diaphragm, the layer of muscle that separates the organs within the chest from the organs within the belly. The oesophagus, the tube that carries food from the mouth to the abdomen, passes through a hole within the diaphragm. In people with a hiatal hernia, the abdomen pushes up through that hole, too.