Heated things are warmed up, like a heated swimming pool or a heated bowl of tomato soup.
After a long walk in the snow, the warmth of a heated building feels great, although tasting a meal that's been heated in a microwave too long doesn't feel too great when it burns your tongue. When heated describes an argument, discussion, or dispute, it means "intense, passionate, or agitated." A heated debate between presidential candidates might be exactly what voters hope to see.