Heartburn is the most common ailment of the esophagus. Officially known as reflux esophagitis or gastroesophageal reflux disease (GERD), heartburn is caused by acidic stomach juices irritating the lower esophagus. Normally these digestive chemicals remain in your stomach until they pass downward into the intestines. But when the valve at the top of your stomach (called the lower esophageal sphincter (LES)) doesn't close, they can reflux upward. Unlike the stomach lining, the lower esophagus is not protected from the corrosive effects of stomach acid. The result is a chemical burn.
If you feel a burning or aching under the breastbone, particularly when lying down after a big meal, you probably have reflux esophagitis. It's called "heartburn" because it feels as if it's coming from your heart. In fact, a hundred years ago doctors thought a heart attack was "acute indigestion." So if your "indigestion" doesn't go away with antacids, or it occurs after exercise rather than eating, better get it checked out. Other clues to heart problems include shortness of breath, sweating, and radiation of pain to the neck, jaw, back, shoulder or arms.
The most common cause of reflux esophagitis is acid reflux from a relaxed LES. It also can be caused by a hiatal hernia, a portion of the upper stomach that is above, rather than below, the diaphragm. Normally, your LES is at the level of the diaphragm, separating the esophagus from the stomach and keeping everything in its place. But in some people, it has moved upward, where it is less able to do its job.