DefinitionHiatal hernia is a condition in which a portion of the stomach protrudes upward into the chest, through an opening in the diaphragm. The diaphragm is the sheet of muscle that separates the chest from the abdomen. It is used in breathing.Alternative NamesHernia - hiatalCauses, incidence, and risk factorsThe cause is unknown, but hiatal hernias may be the result of a weakening of the supporting tissue. Increasing age, obesity, and smoking are known risk factors in adults.Children with this condition are usually born with it (congenital). It is often associated with gastroesophageal reflux in infants.Hiatal hernias are very common, especially in people over 50 years old. This condition may cause reflux (backflow) of gastric acid from the stomach into the esophagus.SymptomsChest pain