In hot summer days like this, your dog cannot sweat to keep from overheating.  When his temperature rises, he pants and drools to keep himself cool.  This forces air over his naval cavity and over his wet tongue.  As the air circulates, moisture evaporates taking some of the dogs body heat with it. When your dog exercises in the hot weather, he may pant for what seems like a long time, a half hour or longer is not unusual.  You should always keep an eye on your dog to make sure that he is not in distress. Symptoms of heatstroke include accelerated and abnormal breathing and heart rate, a dry mouth and heavy drooling. If you notice any of these signs, do not try to give him any pet medication, call your veterinarian right away.