The esophagus is a muscular tube that takes food from the pharynx to the stomach; no digestion takes place here. Peristalsis of the esophagus propels food in one direction and ensures that food gets to the stom-ach even if the body is horizontal or upside down. At the junction with the stomach, the lumen (cavity) of the esophagus is surrounded by the lower esophageal sphincter (LES or cardiac sphincter), a circular smooth muscle. The LES relaxes to permit food to enter the stomach, then contracts to prevent the backup of stomach contents. If the LES does not close completely, gastric juice may splash up into the esoph-agus; this is a painful condition we call heartburn, or gastroesophageal reflux disease (GERD). Most people experience heartburn once in a while, and it is merely uncomfortable, but chronic GERD is more serious. The lining of the esophagus cannot withstand the cor-rosive action of gastric acid and will be damaged, per-haps resulting in bleeding or even perforation. Medications are available to treat this condition.