Heartburn is the most common symptom of a condition called Gastroesophageal Reflux Diseae or acid reflux (GERD).  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.
There are several factors that influence the frequency and severity of acid reflux such as the ability of the LES muscle to open and close properly, the type and amount of stomach juices, the clearing action of the esophagus, the acid-neutralizing effect of saliva and other factors.
What is heartburn?
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. Some people may feel like a bitter or acid taste.
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. Although rarely life threatening, frequent or severe heartburn can limit daily activities and may lead to further complications.
 What are the complications of long-term heartburn?
Acid reflux can sometimes result in serious complications.
Esophagitis, an inflammation of the esophagus that can lead to esophageal bleeding or ulcers.
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.
Lung problems can also develop when reflux causes stomach fluid to overflow into the breathing tubes in which often occurs at night and may cause wheezing, bronchitis and pneumonia.
Diagnosis of reflux
There are various tests used to diagnose reflux are:
Upper GI Endoscopy- The endoscope is passed into the esophagus and stomach to inspect the lining visually. If necessary, a biopsy can be taken for further testing.
Upper GI Series- The patient drinks liquid contrast to coat the esophagus and stomach, and x-rays are taken.
Esophageal Manometry- A specialized tube is passed into the esophagus to measure esophageal muscle function.
24-hour pH monitoring-  A very thin tube is passed to the bottom of the esophagus to measure the amount of acid reflux. The test is performed for 24 hours while the patient goes about normal activities including eating. The episodes of acid reflux can be compared with symptoms reported by the patient.
 How to avoid heartburn (Reflux: GERD)
Avoid lying down right after eating and within two to three hours of bedtime.
Elevate the head of the bed four to six inches.
Lose weight if overweight.
Stop smoking.
Avoid eating large meals. Instead, eat smaller, more frequent meals.
Avoid : Chocolate, coffee and alcohol, fried and fatty foods, mint products, Carbonated beverages, aspirin and most pain medicines (other than acetaminophen).
Choice of treatments
medications:
Over-the-counter antacids- They neutralize stomach acid and can be taken as needed to relieve mild heartburn symptoms. Because antacids are short acting and do not prevent heartburn, they are less useful for severe heartburn.
Medications that decrease reflux from occurring- These medications are designed to tighten the esophagus/stomach barrier or improve stomach emptying to decrease reflux. These medications are sometimes useful but usually less effective than the potent acid blockers.
Medications that block acid production- These medications treat acid reflux by decreasing stomach acid output. They do not work as quickly as antacids but are far more effective because they prevent acid reflux for many hours at a time.
Surgery:
Surgery and other procedures- Most people with heartburn can be successfully treated with lifestyle and dietary modifications and medication. A few may require surgery (fundoplication) to tighten the LES muscle when medications are ineffective.n
Source: Bangkok GI & Liver Center