Girl with Chest Pain?

For the last Mo. My 11 year old daughter has been having leg cramps and pain on on exertion, then she started having chest pain on exertion and very tired, after many test they said her potassium was low. She had a CT. found spot on lung. We –r- going to a heart and lung specialist, any ideas what is going on?

She is not a smoker, yes there is heart prob. in the family, the lung spot is the size of a BB, her blood work other then the potassium her blood work is good. we have takening her off all sports, Sports she was doing was cheerleading. danceing, band. Also when she gets tired she over eats, she is 68 pounds and tall for her age.