Heat is never something you want to play chicken with. I haven't had anything on the bike, but out playing club soccer a few years ago, the thermometer was pushing on 100. And after a full day of tournaments I'll tell you, I was just about done with that day. But long story short, some time during the second half my a blur showed up in my right eye, it got so bad that when I looked down I couldn't see the ball just a patch of blurry grass. That's when I knew it was time to get out. My vision got worse and worse through the rest of the game even sitting in the shade and drinking all the fluids I could. My toungue and fingers got numb and I kid you not, I thought something was wrong with me.

Now, I have a proper respect for exercising in the heat and make sure I drink plenty of water anytime heat starts playing a roll.