Overheating can kill your pet. Never leave an animal in a car since the temperature can rise so rapidly even with windows open. If you're traveling carry cold water to cool your pet. Be sure to rinse them off after swimming, and keep them in a shaded cool area when they are on the beach. Exercise your pet in the cooler hours.
Swimming is wonderful exercise, and it's cooling as well.
Do not leave a dog outside on the hot tar. He's is much lower to the ground and heats up faster. Make a shaded shelter available to your pet in the summer, and always make sure they have water, and it is kept in the shade as well. No one wants to drink hot water. Old and overweight animals have a more difficult time in the heat, make considerations for them, and keep them inside if possible.