About ten to twenty percent of American adults have heartburn at least once a week. About one third have it at least once a month. The statistics are even higher among pregnant women and the elderly.

Something so common can't be serious, right? Wrong. An occasional attack of heartburn is, in fact, nothing to worry about.  Heartburn is not a disease. But frequent and persistent heartburn could be a symptom of a more serious condition that is a disease: gastroesophageal reflux disease, known as GERD. GERD can be diagnosed and treated – and should be, or it could lead to even more serious conditions.

Let's begin with some definitions. Gastroesophageal refers to the stomach and the esophagus. The esophagus (also called the gullet) is the tube that connects the throat to the stomach; when you eat, food goes from your mouth into the esophagus and then down to the stomach. Around the bottom of the esophagus, where it enters the stomach, is a band of muscle called the lower esophageal sphincter (LES). 

Normally, the LES tightens to prevent the contents of the stomach (including food, fluids, and digestive juices called "acids") from leaking back into the esophagus. This process of leaking back is called reflux. Reflux happens when the LES relaxes or opens at the wrong time.

"Heartburn" has nothing to do with the heart. It's actually simple reflux - acid and fluids from the stomach backing up into the esophagus. Heartburn's main symptom is a pain or burning sensation in the center of the chest, usually in the lower part of the mid-chest, behind the breastbone, in the solar plexus or mid-abdomen.

The stomach acids irritating the esophagus cause the pain. Sometimes the burning sensation can be felt in the throat; sometimes the bitter, sour, unpleasant taste of digested food and fluids can be tasted in the back of the mouth; and sometimes the acids end up being regurgitated (spat out). That's why heartburn is also known as acid indigestion and, more technically – and accurately – as acid reflux and gastroesophageal reflux (GER). 

GER is not the same as GERD. GER is simple heartburn. But frequent (more than twice a week), persistent, and severe heartburn can be a symptom of GERD. Among other things, tissue in the esophagus can be damaged by the repeated contact with stomach acids.  When this happens, the condition is known as esophagitis or erosive GERD. (When symptoms are present but there is no tissue damage, the condition is called non-erosive GERD.)

People of any age, including children and infants, can have GERD. The symptoms vary from case to case, and sometimes there are no obvious symptoms. The disease is discovered only because of complications that lead to a thorough medical exam. On the other hand, most people with GERD have very mild symptoms with no tissue damage and little chance of serious complications.