Despite its name, heartburn has nothing to do with the heart (although some of the symptoms are similar to a heart attack). Heartburn is an irritation of the oesophagus caused by acid that refluxes (comes up) from the stomach. Heartburn is also a symptom of more serious gastro-oesophageal reflux disease (GORD).

When swallowing, food passes down the throat and through the oesophagus to the stomach. Normally a muscular valve called the lower oesophageal sphincter (LOS) opens to allow food into the stomach (or to permit belching), then it closes again. Then the stomach releases strong acids to help break down the food. But if the lower oesophageal sphincter opens too often or does not close tight enough, stomach acid can reflux or seep back into the oesophagus, damaging it and causing the burning sensation we know as heartburn.