My 14 yr old son has rapid heart rate. It happens only periodically but really races when it does. Should I be concerned? He's healthy & active.

Possibly. The most common causes of racing heart rate in children is stress/anxiety. Also common is supraventricular tachycardia (svt) which is a racing heartbeat that starts suddenly, often with no obvious trigger. Other arrhythmias (abnormal heart rhythms) are rare but occasionally occur. Dehydration, overexertion and many medications can also cause a racing heartbeat. A cardiologist can sort it out.
Yes and no. It is probably a benign situation. That said, you should have it checked out to be sure.