Acid reflux is a common condition that features a burning pain, known as heartburn, in the lower chest area. It happens when stomach acid flows back up into the food pipe.  At the entrance to your stomach is a valve, which is a ring of muscle called the lower esophageal sphincter (LES). Normally, the LES closes as soon as food passes through it. If the LES doesn’t close all the way or if it opens too often, the acid produced by your stomach can move up into your esophagus. This can cause symptoms such as a burning chest pain called heartburn. If acid reflux symptoms happen more than twice a week, you have acid reflux disease, also known as gastroesophageal reflux disease