A hiatal hernia occurs when part of your stomach pushes upward through your diaphragm. Your diaphragm normally has a small opening (hiatus) through which your food tube (esophagus) passes on its way to connect to your stomach. The stomach can push up through this opening and cause a hiatal hernia. In most cases, a small hiatal hernia doesn't cause problems, and you may never know you have a hiatal hernia 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, although a very large hiatal hernia sometimes requires surgery.