The best thing to do is to leave your pet at home. Properly ventilate your home or turn on the air conditioning. If you keep your dog in a crate, make sure you do not cover it completely.
You can also cool off your dog by placing a cool wet towel on the floor for him to sit on. It'll cool them off quicker from their bottoms.
This may seem like common sense, but lots of pet owners are not aware of the differences in their pets safety and comfort. Take good care of your pets and have a wonderful summer!