I think the main problem with hunting in the heat is that the deer aren't going to be moving that much (at least out in the open). If you're hunting fields, then I doubt you would see anything until it's dark, and you won't be able to shoot. If you're deep in the woods and--like chris149 said--there is a water source nearby, then you should be good to go out. Then again, no matter where you are hunting, your best chances would be in the early morning or late afternoon, when the weather is beginning to cool. Good luck!