An operation to repair an abnormal condition (gastroesophageal reflux) in which stomach acids back up into the esophagus, damaging its lining and causing pain. The procedure involves tightening of the lower esophageal sphincter (valve) so that stomach juices cannot How up into the esophagus, causing a person to have chronic heartburn. Gastroesophageal reflux disease may be caused by an abnormality of the lower esophageal sphincter, which may be too weak to prevent leaking from the stomach into the esophagus. Some people with gastroesophageal reflux disease have a hiatal hernia, a condition in which a portion of stomach protrudes abnormally through the diaphragm.