Heat prostration, more commonly known as heat stroke, is a potentially fatal disease for any breed of dog, even those that are used to hot climates. Heat stroke in dogs is very similar to the condition seen in humans and occurs when the dog's internal cooling system is not able to sufficiently regulate the body temperature, leading to heart failure and death.
The breeds that are at the greatest risk for heat stroke are very active large or giant breeds and breeds that have the pug-type nose known as brachycephalic dogs. In the pug-nosed breeds the air passages that cool the air in the nose are too short to allow for proper temperature changes, resulting in breathing problems and extra stress on the body in extreme heat conditions. In the larger, active breeds the dogs simply don't realize that they are overheating until it is too late and they have begun to have problems in functioning.
One of the worst possible causes of heat stroke is dog's left in cars in the heat. Any dog left in a car in the sun with outside temperatures over 90 degrees Fahrenheit can die from heatstroke in less than 20 minutes. If the dog is already ill, overly warm or stressed by being left alone in the vehicle or just coming in from exercising they can start to have difficulties in a much shorter time. Dogs that are exercising outdoors in the sun may take longer to develop the initial signs of heat stroke or they may be more gradual in developing, but will still be just as serious if not treated immediately.
A dog's normal temperature is somewhere between 99.5 and 102.5 degrees Fahrenheit. At above 103 degrees the dog will start to exhibit signs of heat stroke that will include excessive panting and drooling, loud rasping or roaring sounds when breathing, trouble walking, fainting, disorientation, weakness, loss of balance and eventual collapse. When a dog's internal temperature reaches 107 degrees this is a serious emergency as body function will begin to fail at this point.
At the first signs of heat stroke immediately get the dog to a cooler area. The shade is acceptable, but an air conditioned area is even better. Offer cool but not ice cold water and allow the dog to drink as much as he or she wants. Keep the dog in the cool place until the body temperature is back to normal and breathing is regular and steady. In cases where the dog has already collapsed or is showing disorientation or weakness, additional cooling will be needed immediately. Rinse the dog with cool but not ice cold water. Keep the water flowing over the dog's body and neck, but not over the head. Typically at this stage the dog will not drink however it is fine to offer water, just focus on the cooling rinse or bath. Immediately call the vet or get the dog to an emergency clinic.
Since this is such a serious condition and is fatal, consider carefully monitoring your dog with regards to activity in the heat of the day. Only walk to the dog or provide exercise in the cooler morning and evening hours, always provide shade and lots of fresh, cool water when the dog is left outdoors and even carry water with you on hikes or long walks. Be sure to stop along the way and offer the dog a drink whenever you take one.