Heartburn is a term used to describe gastroesophageal reflux disease (GERD), an uncomfortable, burning sensation in the upper chest or throat that occurs when the contents of the stomach back up and re-enter the esophagus. Most people have, at one time or another, experienced a minor episode of GERD after eating.
However, in people who frequently experience heartburn, the muscular valve at the base of the esophagus (the lower esophageal sphincter) that normally keeps acid out may have a tendency to relax. This allows the acidic contents of the stomach to travel upwards and re-enter the esophagus, causing irritation, burning and sometimes a feeling of indigestion.