What Causes Heart Palpitations In A Child?

My two year old daughter has been waking up screaming in the night. When I went to check on her last night, I noticed that her heart beat would stop and then pick up again. There seemed to be no regularity to this at all. It might have happened about twice in one minute. Today everything sounds normal. I was told that it was common and probably nothing to worry about, but I m worried. I had a cousin die when she was 9 years old during a heart transplant surgery. What should I do?