Heartburn occurs when stomach acid seeps out of your stomach and moves up into the esophagus, your swallowing tube. That's why it feels like burning in your chest. Any food that increases acid can produce heartburn. So can foods that relax the muscle that controls flow between the stomach and esophagus. That circular band of muscle is the lower esophageal sphincter (LES). Avoiding the most common offenders can help you avoid heartburn.