Airlines normally don't allow animals in the passenger cabin. However, live animals are always transported in a cargo bay that is heated and pressurized, because else they wouldn't survive. At the usual flight level of 30.000 ft oxygen levels are way to low and it's -50C.
The only way to fly your dog is by using the pet airlines. A pet airline like Aegean Airlines is the best when it comes to flying your pet. They carry a maximum of up to 32 kilos (66.1387 lbs). You can check out http://www.petfriendlytravel.com/airtravel for more information.