Heat Exhaustion or "heat stroke"

Due to their “cobby” build and dense double coat, every chow is a potential victim of heat stroke if left for prolonged periods in HIGH temperatures.

The leading cause of heat exhaustion, and its advancing into heat stroke; is leaving a dog in a hot car.
Even on a mild day (75-80 degrees F), the temperature inside a car can raise up to 130 degrees rather quickly.

Leaving a window slightly open will not prevent heat build-up. Leaving a dog in a car on a warm day is a risk to the dog's life.

Chows may also fall prey to stress-induced heat stroke. If they become tense or nervous, panting excessively, and cannot maintain a normal body temperature, even in cooler weather, they have been known to heat stroke.

This condition can be fatal!

Cool your chow down by placing him in a bath tub and shower him with cooling water, not freezing as this can induce shock, the temperature must be reduced slowly. 
Once in a stable enough condition seek veterinary assistance at the earliest opportunity.

Alternatively wrap him in cold wet towels and transport him directly to your vet.