In general, with plenty of water, air circulation, and shade, most dogs will probably do okay in warm temperatures up to about 90˚F. However, there is no hard and fast rule about a temperature limit. Dogs do not sweat; they cool themselves primarily through panting. If it gets hot and humid enough, no amount of panting will do the trick. Plus, self-cooling ability depends on the dog. Brachycephalic dog breeds (short-snouted like bulldogs or pugs) cannot cool themselves as easily through panting. Dog breeds that originated in cold climates (like Huskies, Malamutes, Samoyeds, and Newfoundlands) typically have a harder time adjusting to the heat.
Until you know your own dog's tolerance to heat, you should avoid leaving him unsupervised.
There are several things you can do to keep your dog cool as temperatures rise. Indoor and outdoor dogs will benefit from cooling dog beds. Outdoor dogs might enjoy a kiddie pool or tub full of cool water. You can also offer your dog chilled treats to keep him cool. One of the most important things to do is to observe your dog during the hottest times of the day and see if he or she acts distressed and/or is excessively panting. If so, adjustments should be made to cool the environment or move the dog to a cooler location. If any signs of heat stroke or other illness appear, contact a vet immediately. Remember to take the proper steps to keep your dog safe all summer long.