Gastroesophageal Reflux Disease (GERD) is a term used to describe several digestive conditions with different degrees of severity. These conditions are caused by the regurgitation or back-up of stomach acid into the esophagus (the food tube which connects the mouth to the stomach). Heartburn is the most common symptom of GERD. Although many people have occasional heartburn, when it becomes almost constant, the condition is a more serious problem, called reflux esophagitis. If the lower esophagus is exposed to too much acid over a prolonged period, the area can become badly damaged with ulcers and strictures.