Heartburn is a burning sensation that individuals can experience behind their sternum. Heartburn occurs when acid rises up to the esophagus and that organ is not as well protected from acid as is the stomach. When there is a problem with the barrier between the stomach and esophagus (due to a weak esophagogastric sphincter), the person may have gastroesophageal reflux disease (GERD). Here the stomach contents frequently reflux back into the esophagus, and this causes bothersome symptoms or damage to the esophagus. Heartburn due to GERD typically occurs soon after meals and worsens when lying on your back or bending over. Individuals with GERD may also complain of regurgitation of sour stomach contents into their mouth. Functional heartburn is burning behind the sternum without evidence of GERD or esophageal motility disorders as the cause. Individuals with functional heartburn do not respond to the usual acid-suppressing treatments for GERD. It is thought that these individuals have increased sensitivity to reflux or even normal amount of acid which may lead to symptoms that other individuals would not experience.