A dog rids its body of excess heat by panting. On a hot day, a dog must take in more air to keep its temperature constant. For this reason, a hot, enclosed space with little air circulation, such as the inside of a car, is a dangerous place for a dog. On a summer day when the outside temperature is 85 degrees, the interior of your car can reach 120 degrees in just 30 minutes, even with the windows partially open. Because a dog's normal body temperature is about 102 degrees Fahrenheit, the dog will suffer brain damage or death if its body temperature rises to 107 degrees. High humidity can make the situation worse by reducing a dog's tolerance to heat even at relatively low temperatures.
Animals locked inside a car, even for just a few minutes, are at extreme risk of heatstroke -- even with the car windows open. Dogs in poorly ventilated garages and very young, old and obese dogs left outside on hot days are susceptible to heatstroke as well.
To prevent heatstroke, limit your pet's physical activity to the evening or early morning, while the day is cool. Never force a dog to exert itself in the heat; you may not notice that the dog is overheated until it is too late. Remember that Newfoundland have a strong drive to be with humans. If you're having fun in the sun, make sure that your dog doesn't spend all day laying beside you out of loyalty. Provide shade or take the dog inside when he's had enough.
Signs of heatstroke include excessive panting and salivation, elevated temperature, an anxious expression, warm foot pads, vomiting and diarrhea. If you notice these symptoms, act quickly by pouring cool water over your dog or put ice packs on the animal's head. Get him to a veterinarian right away.