Since dogs obtain a fair amount of evaporative cooling through heavy panting the dog's mouth can be moistened. A hot dog should not stand around in a muzzle. The muzzle can seriously interfere with panting. Dogs in heat stroke may feel clammy to the touch. While going into heatstroke they may produce copious quantities of thick, ropey saliva.
Seizures can be a consequence of heat stroke.
Dogs are more sensitive to heat and high humidity than humans. A situation that may be merely very uncomfortable for you may kill your dog. Dogs take longer to acclimate to climatic changes involving increased heat and humidity than people and they will loose that acclimation over a period of cool weather. Judges at lure coursing events should keep in mind that the larger and faster breeds are much more susceptable to heat stroke than small breeds and deport themselves accordingly in relation to reruns and starting courses over. In my opinion mid summer trials should have copious shade and water available or be limited to Basenjis, Pharaoh Hounds and Ibizan Hounds.