Neighbors say paramedics took two people to the hospital Tuesday morning in suburban Delray Beach.
They say firefighters found high levels of carbon monoxide in their duplex.
Palm Beach County Fire Rescue responded to the residence on Whippet Way just before 9 a.m.
Neighbors say a man left his car running and exhaust filled the duplex.
Firefighters could be seen ventilating the building before leaving.
Officials at Delray Medical Center said one woman living in the duplex was discharged from the hospital.
The man taken to Delray Medical Center remains in the hospital in fair condition.