A hiatal hernia (also called a hiatus hernia) is a condition in which a portion of the stomach bulges and protrudes upward through an opening in the diaphragm. The diaphragm is the sheet of muscle that separates the chest from the abdomen. Hiatal hernia symptoms include heartburn, belching, difficulty swallowing, and chest pain. A weakened or enlarged hiatus (the hole in the diaphragm through which the esophagus passes) may increase the risk for developing a hiatal hernia, but a definite cause is not known.

A hiatal hernia develops when the hiatus (a hole in the diaphragm through which the esophagus passes) becomes weakened and allows a portion of the stomach to herniate (move upward) into the chest cavity. Because the hiatus is involved, hiatal hernia is often called hiatus hernia.

The two main types of hiatal hernia are a sliding hiatal hernia and a paraesophageal hiatal hernia. In a sliding hiatal hernia, the herniated portion of the stomach protrudes above the diaphragm and slides in and out of the chest. Most sliding hiatal hernias are very small and cause no symptoms. Sliding hiatal hernia symptoms, if they do occur, are usually minor and symptoms include gastroesophageal reflux and indigestion. In a paraesophageal hiatal hernia, the upper portion of the stomach is pushed above the diaphragm and lies beside the esophagus. A paraesophageal hiatal hernia may become a serious and painful medical condition if it gets stuck or pinched by the diaphragm and loses its blood supply. Of note, the symptoms of paraesophageal hiatus hernia can be milder than those caused by a sliding hiatus hernia.