Stomach acid going back to oesophagus (food pipe) gives heart burn. Docotr may give medication for acidity. In the mean time ask him to sleep on left side so that stomach is below food pipe. Stomach acid will not go up in the food pipe. However he needs treatment for acidity. For heart burn see a gastroenterologist.
Heartburn? Heart issues? He could run the situation by his doctor and see if his doc wants to do a stress test to make sure.