My 4.5 year old boy is sleeping and his hart rate is 120 a min is it a concern he has also bin sleeping most of the day?

Pulse ok: but a little faster than expected for a child his age while sleeping. Of more concern is why he is sleeping most of the day. Mild fever, slight dehydration or mild infection will cause the pulse to increase proportionately, but in itself doesn't explain his sleepiness. Infection?? Headache?? Please get him evaluated if he doesn't improve. Meanwhile, push fluids.

YES: That is an elevated heart rate and it sounds like your child may be ill. The heart rate is often the first thing to change in children during illness. I would contact your doctor ASAP and have this situation checked out STAT