The fire broke out in a top floor apartment in Norwood.
Firefighters were met at the door by flames.
After fighting their way in, they discovered a 37-year-old man unconscious.
Emergency crews rushed him to the hospital in critical condition.
No firefighters were injured but they had a hard time dealing with the stifling heat.
Several pets in the building were also found unconscious.
Investigators believe the fire started in the apartment's kitchen.
The cause of the fire is under investigation.