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. Acid reflux is also known as heartburn, acid indigestion, or pyrosis. It happens when some of the acidic stomach contents go back up into the esophagus. Acid reflux creates a burning pain in the lower chest area, often after eating. Lifestyle risk factors include obesity and smoking.