Gastroenterology Consultants,SC: Diseases of the GI tract HEARTBURN AND REFLUX (GERD) [<<back | list all>>] Heartburn occurs when stomach acids flows upward (regurgitates) into the esophagus. The esophagus is the tube that carries food to the stomach. People usually feel heartburn as a burning sensation or pain behind the breastbone. When the LES muscle does not completely close and stomach juices seep back into the esophagus, this is known as reflux.