I make sure that I drink a lot of water when I ride and it's hot. You can take electrolyte pill type of things to help with dehydration. Eight miles isn't too bad.. dress light, drink often, and take it easy. I LOVE riding in the heat. We did 50 miles of winding, hilly roads on Saturday, temps were 100-104. Did just fine. Today, high temps again, and I plan on a climb this afternoon. 13 miles, 3,100 feet. Cooler at the top, but takes some effort in the heat to get up there!
Just take care, listen to your body.
A ship is safe in harbor, but that's not what ships are for.