From Wikipedia, the free encyclopedia. A hiatus hernia or hiatal hernia is the protrusion (or herniation) of the upper part of the stomach into the thorax through a tear or weakness in the diaphragm. Hiatus hernias often result in heartburn but may also cause chest pain or pain with eating. The most common cause is obesity. The diagnosis is often by endoscopy or medical imaging. A hiatus hernia may be treated with lifestyle changes such as raising the head of the bed, weight loss, and adjusting eating habits.