LES (Lower Esophageal Sphincter) is the valve that allows food and liquid into the stomach and close immediately after that. It prevent the reflux of stomach acid entering into the esophageal. If you find your stomach producing too much of acid, this acid can back up through the valve and in to your esophagus. In such case you will sense a burning and painful sensation in your chest called heartburn. Dyspepsia and regurgitation are other symptoms of acid reflux.
You might be suffering from GERD (Gastro Esophageal Reflux Disease) if the symptoms occur at least 2 times a week. It can be caused by your food choices, certain types of meditation, and genetic abnormalities in your stomach.