Gastroesophageal reflux disease (GERD) is a common disease in western countries. In the United States, 7% of the population experiences heartburn daily and 44% at least once a month.[2] Heartburn occurs when esophageal mucosa is exposed to the acidic gastric content, but the complaint of heartburn is not always a reliable guide to the presence of acid reflux in the esophagus.[3] Further, only half of the patients with increased esophageal acid exposure will have esophagitis.[4] Therefore, the diagnosis of gastroesophageal reflux disease (GERD) on the basis of symptoms or endoscopic findings is problematic.