The lower esophageal sphincter (LES) gets closed after the passage of food. If LES is not properly closed or gets opened quite often, the acids produced in the stomach moves up to the esophagus. As a result, you will suffer from heart burn.
Some of the acid reflux causes include intake of snacks before going to bed, consuming onions, chocolate, citrus, fatty foods, tomato, and mint. You may also suffer from acid reflux if you lie down after intake of a large meal.