http://www.aboutsmalldogbreeds.com/brachycephalic-dog-breeds.html

Love brachycephalic breeds like pugs, bulldogs, boxers, etc?  These types of dogs make wonderful pets but they need special care.  Brachycephalic breeds or "short snout breeds" require owners who are prepared to have an indoor only pets.  These breeds have a decreased ability to regulate temperature due to their shortened snout.  Therefore, if you are an owner with a brachycephalic dog please make sure to keep them inside in the air conditioning when the weather gets hot!

For more information check out these websites:
http://www.aboutsmalldogbreeds.com/brachycephalic-dog-breeds.html
http://pethealthlibrary.purinacare.com/articles/dogs-articles/brachycephalic-dogs-brachycephalic-syndrome/