Heatstroke is very common for pets as they have trouble keeping their bodies cool especially when the surrounding temperatures are extremely hot. Since your pet can not sweat to regulate body temperature they have to pant to get rid of excess heat. When the outside air temperature is equal to or higher than a pet's body temperature which is 99 F - 102.5 F or if the pet is in the sun, heat stroke can occur. If first aid is given immediately your pet will likely recover within an hour. If the body temperature is above 105 F your pet can go into shock and have organ failure. In this case provide first aid and get emergency vet assistance.