Heartburn Causes. Heartburn is actually a symptom of GERD (gastroesophageal reflux disease), and is caused by acid refluxing back into the esophagus. Risk factors include those that increase the production of acid in the stomach, as well as structural problems that allow acid reflux into the esophagus. A hiatal hernia where a portion of the stomach lies within the chest instead of the in abdomen, can affect the way the LES works and is a risk factor for reflux. 2  Hiatal hernias by themselves cause no symptoms. 3  It is only when the LES fails that heartburn occurs.