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.
What Does Heartburn Feel Like?

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.
Is Heartburn Caused by Hiatal Hernia?

Hiatal hernia is a common condition that occurs when the stomach partially sits in the chest cavity through a weakness in the diaphragm. A persistent hiatal hernia may produce significant heartburn. However, many people who experience heartburn do not have a hiatal hernia. Likewise, many people with a hiatal hernia do not experience heartburn. Testing and therapy usually focus on the heartburn rather than on the hiatal hernia.
Is Heartburn Serious?

Usually not. Heartburn and reflux are very common, with 10 percent of the population experiencing these symptoms at least once a week. For example, 25 percent of pregnant women have heartburn or experience heartburn-related symptoms. Although rarely life threatening, frequent or severe heartburn can limit daily activities and productivity and may lead to further complications. However, with proper understanding of the causes of heartburn and a consistent treatment program, most people find relief.
What are the Complications of Long-Term Reflux and Heartburn?

Acid reflux can sometimes result in serious complications. Esophagitis, an inflammation of the esophagus that can lead to esophageal bleeding or ulcers, can occur as a result of frequent exposure of the esophagus to stomach acid. In addition, a narrowing or partial closure (stricture) of the lower esophagus may occur, interfering with a person’s ability to swallow. Some people develop a condition known as Barrett’s esophagus, a change in the cells of the tissue lining the bottom of the esophagus that can increase the chance of developing cancer. In most cases, individuals with Barrett’s esophagus should be monitored with periodic upper GI endoscopy and biopsies. Lung problems can also develop when reflux causes stomach fluid to overflow into the breathing tubes. This often occurs at night when a person is lying down and may cause wheezing, bronchitis and pneumonia. Other possible problems caused by acid reflux include inflammation of the throat, voice box and airways.