Acid reflux occurs when stomach acids regurgitate up into the esophagus, essentially a tube that connects the throat to the stomach. Once the acid starts burning the muscle lining in the esophagus, a person may start to feel pain and discomfort in his or her chest. This is called heartburn. It is a cause-and-effect relationship: acid reflux may cause heartburn, but heartburn cannot be experienced without acid reflux.
Heartburn and acid reflux may occur due to a variety of factors, including over-consumption of acidic foods, obesity, smoking, stress, even tight clothing. Occasional bouts of heartburn and acid reflux are normal and not a cause for too much concern. When acid reflux happens frequently, however, it is called acid reflux disease or gastroesophageal reflux disease (GERD) and usually requires medical treatment by a physician.
To best understand how heartburn and acid reflux are related to each other, it helps to understand how the esophagus works and its role in the digestive process. When food enters the mouth, saliva breaks down the starch components on the food. The food molecules, broken down by the chewing and salivation process, then pass through the esophagus, a tube about ten inches (25.4 centimeters) long. Muscles alongside the esophagus’s lining help push the food further down.
The esophagus is connected to the stomach through a ring of muscle, called the lower esophageal sphincter (LES). The LES functions as a one-way valve, so food can enter the stomach but cannot get back the other way — at least, that’s the way it is supposed to happen. Once the food enters your stomach, glands inside the stomach continue the digestion process by secreting acids that further break down the food molecules. During this stage, the LES is supposed to hold all that food and stomach acids inside the stomach. However, sometimes the LES doesn’t close properly, is too relaxed, or it doesn’t close at the right time. If too much food is consumed, the pressure from inside the stomach is sometimes more than the LES can handle. Thus, the stomach acid goes back up the esophagus, and heartburn and acid reflux occurs.
Acid reflux doesn't necessarily cause pain or discomfort every time. When the acid reflux is particularly bad, however, stomach acids can eat away at the lining of the esophagus. This normally results in a burning pain and a feeling of discomfort in the chest area. This is commonly known as heartburn, though in reality, the heart has nothing to do with the pain. Common instances occur of people experiencing heartburn pain and believing they are having a heart attack.