Welcome to JustAnswer!
Increase in the heart rate occurs when someone has fever. For every one degree rise in temperature, an increase of 10 beats is noted.
Also there are certain viral infections which can affect the muscle of heart and also cause fever. In this situation, the increased heart rate is due to involvement of heart and it needs medical attention.
So if you find the heart rate more than 130-140 take him to ER immediately.
Thats how you have to count.
You can also count his pulse rate at his wrist for 6 seconds and multiply by 10.
Give tylenol 6th hourly and sponge him ( which you are doing).
Once the fever settles down, heart rate will come down.