My 10 year old daughter told me she had to stop playing and rest twice during one gym class last week. She said she had shortness of breath and a sharp pain right where her heart is. This past Friday she exerted herself for about 30 seconds playing tag in the swimming pool. She came to me and had me feel her chest. Her heart was beating extremely hard and fast. She was not having pain at the time, but I had her describe the pain, when she does feel it. She said it was sharp, like a knife trying to poke out of her chest. She has always been very healthy and is not overweight at all. I plan to get her checked out, but should I be very concerned?