Hydration is key to riding in the heat. I really don't mind the heat that much until I stop at a traffic light or stop sign, then you really can feel it radiate and you break into a sweat. Keep moving and you will be naturally air-conditioned.

One thing that I've been doing for at least 10 years now is really helpful. If you have an inexpensive digital watch (like a Timex Triathlon) set the "countdown" timer for 10 minutes. When you start out on your ride set the timer and every ten minutes you will get an audible reminder to drink. It is really easy to get into a ride (especially when riding in a group which I do often) and lose track of time and forget to drink. By the time you realize it you've been dehydrating for too long and then it is too late without a long stop to get some fluids in you.

It's become so common for me to set this timer that my riding buddies hear my alarm and they all reach for their bottles and yell out"Time to Drink". It really does help and is so simple to do. I haven't bonked from lack of fluids for years as a result after doing so many times as a newbie rider.

Give it a shot. Cheap insurance instead of dragging yourself home in the heat and suffering needlessly.