Gastroesophageal reflux disease (GERD) refers to acid reflux, or backward flow, of stomach acid and other contents into the esophagus. If stomach acid moves backward up the esophagus, reflexes result in spasm of the airways that can cause shortness of breath and coughing. In some instances, acid reflux can be so severe that substances can be inhaled (aspirated) into the lungs and cause similar symptoms as well as damage to lung tissue. In some individuals, no sensation of heartburn is felt and their only symptom may be cough.