A hiatal hernia occurs when the upper part of your stomach bulges through the large muscle separating your abdomen and chest (diaphragm).
Your diaphragm has a small opening (hiatus) through which your food tube (esophagus) passes before connecting to your stomach. In a hiatal hernia, the stomach pushes up through that opening and into your chest.
A small hiatal hernia usually doesn't cause problems. You may never know you have one unless your doctor discovers it when checking for another condition.
But a large hiatal hernia can allow food and acid to back up into your esophagus, leading to heartburn. Self-care measures or medications can usually relieve these symptoms. A very large hiatal hernia might require surgery.