My 15 year old daughter is an elite athlete. She plays basketball and is extremely fit. When she is completely at rest, on the couch or in a classroom, she has been experiencing a sudden series of rapid heart palpitations. She also says her heart feels heavy before and after the palpitations. They used to happen once a month. She has had it happen 3x a day for the past three days. Yesterday, she said she had a shortness of breath. She is not stressed & does not use caffeine or drugs. What are the possible causes and what tests should we run on her? Thank you.