Yes, my heart rate is usually up to 10 bpm faster than what I would expect for the effort. I haven't been wearing my chest strap in the summer because I prefer to ride completely on perceived effort when it is so hot, I find it helps me regulate better. I have to keep myself from doing too intense of efforts in the heat, last summer I threw up 3 different rides from overheating. Once this year I got to the point of dry heaves. It just isn't worth it and it takes usually 24-48 hours to recover if I overheat that bad, I am weak and feel awful.