Okay i guess i need to rephrase my question my son had been sitting in the car for a 4 hour trip to see his behavioral specialist and as usual the check is heart rate blood pressure weight height and that's when i was informed that he had a very fast hear

Tachycardia : Rapid heart beat can be due to anxiety. Other possible causes in children are arrhythmia or hyperthyroidism. See your primary doctor first. BP should also be checked. Cardiologist next.

Tachycardia: Your question is cutoff so limited info. Let me guess that your son is on some ADHD drug(s) like Ritalin (methylphenidate). These drugs can all cause tachycardias and increased BP. See a pediatrician and review the drug list. They also can interact with a wide variety of things including certain foods. Avoid caffeine like chocolate. They are also problematic drugs for any future surgeries.