Heartburn is the most common symptom of a condition called gastroesophageal reflux or acid reflux. A sphincter (specialized muscle), known as the lower esophageal sphincter (LES), is located at the end of the esophagus and opens during swallowing to allow food to pass into the stomach. The LES muscle then closes quickly to prevent the return (reflux) of food and stomach juices back into the esophagus.
However, the LES muscle does not always work perfectly. Gastroesophageal reflux occurs when the LES muscle either relaxes inappropriately or is weak. This allows stomach juices to back up, or reflux, into the esophagus, creating heartburn. When the acid contents from the stomach regularly back up into the esophagus, a chronic condition called gastroesophageal reflux disease, or GERD, occurs. Heartburn is sometimes called acid indigestion and usually occurs after meals. In addition to heartburn, symptoms of acid reflux may include persistent sore throat, hoarseness, chronic cough, asthma, heart-like chest pain and a feeling of a lump in the throat.
There are several factors that influence the frequency and severity of acid reflux: the ability of the LES muscle to open and close properly, the type and amount of stomach juices that reflux up into the esophagus, the ability of the stomach to empty properly, the clearing action of the esophagus, the acid-neutralizing effect of saliva and other factors.
Heartburn is a burning pain behind the lower breastbone that may radiate upward toward the neck. It may also include the sensation of food or liquid coming up into the throat or mouth (regurgitation), especially when bending over or lying down. These symptoms may be accompanied by a bitter or acid taste.