What should you do with a child with a severe tachycardia?

Pediatrician: There's nothing you can do at home, on your own. Take your child to the pediatrician. The rhythm can be caught on extended monitoring, properly diagnosed, and treated accordingly.

How fast?: I agree with dr. Werner that you should have your child evaluated by his/her doc..But just an fyi: a new born resting heart rate is about 140-160 bpm...This range gets lower and lower to 60-99 BPM as an adult. Does your child have symptoms? I.E feeling palpitations, shortness of breath, dizziness?If so, avoid caffeinated drinks/candies, cold meds etc..Consult doc if u r still concerned. Good luck.