"Indigestion" refers to any number of gastrointestinal complaints, which can include gas (belching, flatulence, or bloating) and upset stomach. "Heartburn" refers to a burning feeling that can be caused by stomach acid regurgitating into the esophagus from the stomach, by gastritis (inflammation of the lining of the stomach), or by an ulcer of the stomach or duodenum (also called peptic ulcer).
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