This is where the heart is located but heartburn has nothing to do with the heart. The burning or pain originates in the esophagus which is behind the heart. The esophagus is a long muscular tube which propels food from the mouth to the stomach. Normally there is an area at the junction of the esophagus and stomach where the muscles are generally tight, relaxing only temporarily to allow swallowed food to pass into the stomach. The LES prevents acid, which is produced in the stomach to help digest food, from being pushed, or refluxing, into the esophagus.
Human stomachs have a special lining which is resistant to the acid produced in the stomach.
Anyone might have occasional brief episodes of heartburn. This is considered normal. It is abnormal when it happens several times during 24 hours, when it happens many times a month, and when it begins to cause swallowing difficulties, hoarseness, coughing episodes, or bleeding. When the acid only goes as high as the middle of the esophagus it usually is felt as heartburn. It can however go as high as the mouth where some people will get a sour or acid taste.