The canine species is typically bad at dispelling body heat and this puts them at higher risk of "heat stroke" which is a life-threatening condition best defined as when a dog's normal body temperature of 101.5 degrees Fahrenheit (F) goes above 105F. Dogs have only a couple of ways of dispelling heat namely, through blood vessel expansion and through panting (and to a much smaller degree through sweating from the pads of their feet).
A responsible dog owner should not only be aware of the signs of heatstroke (heavy panting and rapid breathing, excessive drooling, dry mucous membranes, bright red gums and tongue, skin hot to the touch, and a higher heart rate) but should also be familiar with steps one can take to prevent heat stroke in the first place. These steps include:
If your dog must be outside make sure he has access to plenty of cold freshwater (add ice cubes every so often) as well as shade.
On particularly hot and/or humid days walk your dog early in the morning before the sun has come up all the way and wait until after it starts to set later in the day while avoiding the hottest times of the day between 10 AM and 4 PM except for quick potty breaks.
Test the ground temperature (especially the black pavement) by placing the palm of your hand on the ground. If it's too hot for you to keep your hand there for a bit it's too hot for your dog's sensitive paw pads so walk them where the ground temperature is cooler to the touch.
NEVER leave your dog in a hot parked car!!!
If your dog typically wears a muzzle leave it off since it restricts their ability to pant and panting is one of the ways dogs dissipate body heat.
Carry extra water for both you and your pup during long hikes or walks in hot weather.
(If you have sufficient outside access and you can buy a kiddie pool to fill with water it's a great way for your pup to cool down by standing in the water since dogs sweat through their paws.)
If you suspect your dog is experiencing heatstroke rush him to the vet as soon as possible where he may be given intravenous fluids to replace what he's lost through dehydration.
If getting him to the vet is not possible immediately use a cool cloth or pour cool water (NOT cold) over his head, stomach, armpits, and feet. Then fan him to encourage air circulation. Get him to the vet ASAP!