Heartburn, or reflux, is a symptom of gastroesophageal reflux disease.What is the cause of reflux?

Reflux occurs when stomach contents flow backward into the esophagus. Stomach acid irritating the esophagus causes the burning sensation called heartburn, so the correct choice is stomach acid in the esophagus. Too much peristalsis and a hole in the stomach tissue are not the cause of typical reflux.

AI-written and checked against the verified answer.