Under normal circumstances, the junction (GOJ) between the bottom end of the gullet and the top of the stomach is at the level of the diaphragm (the breathing muscle). In some people the GOJ is above the diaphragm, and so the stomach has been pushed (i.e. herniated) through the opening (i.e. hiatus) in the diaphragm, leading to a hiatus hernia. As a result of this disruption of the normal muscular barrier, acid produced by the stomach may move more freely into the lower gullet leading to gastro-oesophageal reflux disease). A hiatus hernia is usually diagnosed at upper gi endoscopy or less commonly, following an X-ray study called barium swallow.