Oesophageal reflux, also known as HEARTBURN, is a medical condition in which stomach acid flows back up into the oesophagus, causing a burning sensation in the chest. It is caused by a malfunctioning of the lower oesophageal sphincter, which normally prevents stomach acid from entering the oesophagus. Symptoms of oesophageal reflux include chest pain, difficulty swallowing, and a sour taste in the mouth. Treatment for oesophageal reflux includes lifestyle changes, medications, and in some cases, surgery.