Dogs lose heat by panting, so when the environmental temperature is high, dogs overheat far more quickly, and they easily become dehydrated. Listen to this podcast to learn more about how to keep your dog cool and healthy.
The dangers of heat stress and dehydration to dogs in summer – podcast
Please note that I am unable to answer veterinary questions in comments. If you have questions or concerns about your pet's health it is always better to contact your vet.