I noticed smoke filling the inside of my car. I looked over at the passenger seat, and my coat was on fire. I poured my drink on it, pulled over, and threw the coat out of the car. I saw a large hole in the lumbar area of the passenger seat, and it was glowing red and putting out a lot of heat. The seat heater was on, so I immediately turned it off. It was obvious that the fire has started inside the seat, and there was no other fire source in car--ie. lit cigarette, lighter, etc. If someone had been sitting there, they would have serious burns. The seat will need to be replaced.