Definitely tell the pediatrician about this issue. The next time your nephew experiences these symptoms, make sure someone takes an accurate pulse in beats per minute. It is not all that uncommon for children to have SVT. If a five year old has a pulse rate of 200 or more, it might be SVT and the child should be seen by a doctor ASAP - at the very least, the pediatrician should be called and it might warrent a trip to the ER.
In my experience, if a healthy five year old is running around playing very actively, their heart rate might be around 160-180, but if a child has a very fast heart rate when inactive, it should definitely be checked out by a doctor. Keep in mind though, that a healthy five year old's resting pulse can be as high as about 120 which can be perfectly normal.
Fortunately, children tend to tolerate SVT better than adults, that is, they may not have dizzyness, faintness, etc. But, it is very important to have an accurate diagnosis to rule out more worrisome conditions like WPW.
The Content on this Site is presented in a summary fashion, and is intended to be used for educational and entertainment purposes only. It is not intended to be and should not be interpreted as medical advice or a diagnosis of any health or fitness problem, condition or disease; or a recommendation for a specific test, doctor, care provider, procedure, treatment plan, product, or course of action. Med Help International, Inc. is not a medical or healthcare provider and your use of this Site does not create a doctor / patient relationship. We disclaim all responsibility for the professional qualifications and licensing of, and services provided by, any physician or other health providers posting on or otherwise referred to on this Site and/or any Third Party Site. Never disregard the medical advice of your physician or health professional, or delay in seeking such advice, because of something you read on this Site. We offer this Site AS IS and without any warranties. By using this Site you agree to the following Terms and Conditions. If you think you may have a medical emergency, call your physician or 911 immediately.