In a video posted to the Bakersfield Fire Department's website that has been widely shared online, firefighter Matt Smith is shown carrying the nearly lifeless Shih Tzu from the house on Wednesday.
By the end of the video, Jack is sitting up, alert and looking around, though panting heavily.
He was then reunited with his worried owners, a married couple who were unharmed by the fire.
Jack suffered respiratory tract injuries and burns to his feet, but the dog was doing well on Friday after receiving extensive oxygen therapy, department spokesman John Frando said.
Frando, who shot the video of Jack's rescue, said it looked so dire for the pooch that at one point he stopped recording.
"I thought Jack was going to die," he said. "He was in really bad shape."
Frando said Smith found Jack behind a couch in the home, which was billowing with smoke by the time they arrived.
Smith and Jack were reunited Thursday at the veterinary hospital where he was being treated.