My Husband Has Been In The Emergency Room Three Times

My husband has been in the emergency room three times with chest pain that seems like a heart problem. They have run many, many tests and they only discovered a moderate blockage. Due to his pain, they went ahead and put stents in to rule this out as the cause of the pain. He has continued to have chest pain along with feeling tired and weak (could be medicine related I know). We thought perhaps gall stones but they thought that unlikely and have not done evaluation in this area (his gall bladder was removed several years ago but I heard you could still have gall stones). What else could cause this pain?