Many Bulldogs are relatively heat tolerant. They are smart animals who generally will temper their activity level to the weather. Bulldogs have been known to choose to lie outside in 95 degree heat without problems, even choosing it over air-conditioned space inside. However, their care is your responsibility, so you should be vigilant when your dogs are outside in the heat and make sure they do not get overheated.
If your dog is overheated and/or over excited, it is critical to calm him down, since this can raise the body temperature like a fever does. You should make sure the throat is free of mucous, and minimize the swelling due to heat. Fast action is essential and you generally will not have a real problem if you act quickly rather then letting problems build. It is better to err on the side of caution with these situations: you won't harm the dog with water and ice, but overheating can debilitate and even kill any animal, even humans.
If your dog has a problem, you can clear the dog's throat of mucous with your finger. A squirt of lemon juice will cut through any mucous and clear the throat. Some dogs like the taste of lemon; many hate it. Then give him ice cubes and hold his mouth shut to make him chew them if necessary. Get him to a spot where he can lie calmly out of the heat.
Don't leave your dog outside in the hot sun unsupervised. Don't have him sit around on a leash without access to water while you're socializing if it's warm. Never leave any dog in an enclosed car in the summer - cars turn into ovens really easily in hot weather
You should become aware of the sound and rhythm of the dog's normal breathing and panting. If your dog is over-excited, his breathing will be abnormally fast and hard. If the dog is hyperventilating, his tongue will have a bluish cast instead of the normal pink and it will hang out unusually far. His panting will be heavy, probably with a rasping sound and he may look wild eyed. To treat him, you will need to use some or all of the following: water, ice, lemon juice, and aspirin suppositories.
You can immediately place him in a tub of cold (but not ice) water or in a cold shower. If you're outside, pour water over him - straight from a garden hose if possible. He may not like it, but do it anyway. It's important to get him wet down to the skin so evaporation of the water can speed bodily cooling. Then get him into the shade. You can clear then his throat with lemon juice. Give him ice cubes and hold a compress of ice cubes on his genitals and/or head. If his temperature is high (a dog's normal temperature is about 102 degrees), give him an aspirin suppository.