A hiatal hernia occurs when a small portion of the stomach pushes upward through the diaphragm, a sheetlike muscle that separates the lungs from the abdomen. Usually this doesn't cause any symptoms, but it increases the risk of stomach acid backing up into the esophagus (reflux), which can lead to heartburn.
Normally the entire stomach sits below the diaphragm. The esophagus passes through an opening in the diaphragm called the hiatus before it enters the stomach. Weakened tissues within and around the hiatus allow a hiatal hernia to develop.
A hiatal hernia that is not causing symptoms does not usually need any treatment. Treatment for a hiatal hernia that causes heartburn is the same as for gastroesophageal reflux disease (GERD) and may include home treatment with nonprescription antacids, acid reducers, or acid blockers; prescription medications; or, in severe cases, surgery.
WebMD Medical Reference from Healthwise