Chest pain is common in children. The vast majority of the time it is non-cardiac in origin. Most often it is musculoskeletal due to stretching of joints and tendons in healthy, growing children. Less often it is due to gastroesophageal reflux, or wheezing. Least common is cardiac disease. Your child's pain was not associated with vigorous activity, and if I am correct from your posting, there was no dizziness or passing it; it also sounded fairly brief. So if the ECG was read as normal, and your pediatrician feels that she has a normal cardiac exam, and if there is no family history for inheritable forms of heart disease or early sudden death, then this is most likely non-cardiac chest pain. Most children actually do say "my heart hurts"--why we don't know. A person's heart rate will speed up when they are in pain. In order to differentiate that from an abnormal heart rate, or arrhythmia, your doctor needs to know what the heart rate was at the time of symptoms. So if you can learn how to take a pulse (at rest and with activity) and then compare that to the pulse rate at the time of symptoms that would be very helpful.
Thank you very much for the quick response. I will take her pulse and gather that info for her doctor.