What Causes Tightness In Chest Of A Child?

My healthy 14 yr old daughter has told me her heart hurts. Feels like someone is squeezing it, then lets go, then squeezes it again, etc along with sharp pain. This is continuous. This has lasted for 2.5 hrs tonight. This has happened before. No other symptoms. When she exhales and right before she inhales its a little more intense. Not sure what to think it might be or whats causing it.
Mrs. Howard