In GERD, the valve at the top of the stomach (where the stomach and the esophagus connect) does not close tightly enough. This allows the contents of the stomach to move up into the esophagus. GERD usually causes a feeling of burning, warmth, heat, or pain that often starts in the upper part of your belly, just below your breastbone (sternum). This feeling (called heartburn) may spread in waves upward into your throat, and you may have a sour taste in your mouth. Heartburn is sometimes called indigestion, acid regurgitation, sour stomach, or pyrosis.