one or two summers ago I was heading back from a rather long ride with some friends and the heat had hit us a bit harder than expected. I had hydrated and taken a few extra breaks but after climbing a short hill and decending the other side I suddenly felt a bit tired. Looked at MY HR monitor and noticed it was a bit high. I didn't feel all that bad just a bit weak. After about 1/2 mile on level ground my HR hadn't dropped any. Still didn't feel bad only a bit weak. Pulled up to a stop light and MY HR was still high and it was only then I noticed I wasn't sweating. We found a shady place and poured water over me to cool me down and I got a ride in a truck back to the starting place for our group ride. It was the beginning of heat exhaustion. I only caught it early because I was concerned with my HR reading. Yes I use one and no my chest didn't hurt even with a high HR. But that is just me.