Heartburn is a common disorder of the stomach caused by the overproduction of stomach acid, usually in reaction to a large meal. It is not dangerous and will resolve itself without treatment. An antacid will generally provide relief in a few minutes.
However, the pain of heartburn is often mistaken for symptoms of more serious diseases, and vice versa. An impending heart attack often feels like very bad heartburn. So does a gastric ulcer, and attacks of cholecystitis. If heartburn lasts for more than a short while, or is not alleviated with antacids, medical attention should be sought.
Heartburn is a common complication of pregnancy.