Two men died after they suffered full cardiac arrest, apparently from breathing in smoke. A third resident also had a heart attack, but she survived.
One of the men was in his 30s and the other was in his 40s. The first man was pronounced dead at 9:45 a.m. at the University of Chicago Medical Center and the other died later at Jackson Park Hospital.
The medical examiner's office said it would release their names after an autopsy Wednesday.
The men were found on the seventh floor and the woman was found in the building's lobby Paramedics were able to revive her with CPR and took her to the University of Chicago Medical Center.
A firefighter suffered minor injuries.
The fire broke out about 8:40 a.m. and was quickly deemed an extra-alarm fire with a call for at least 10 ambulances. Firefighters on one ladder battled the blaze on the seventh floor while firefighters on another tried to reach residents on balconies on the other side of the building.
The fire might have started in the bedroom of an apartment on the seventh floor. The blaze spread to an apartment on the eighth floor, he said. It was under control by 9:25 a.m.