A slang term from Arduin, used as a reference to a person's rowdy, boisterous spirit. Its akin to the phrase, "He is full of spit and vinegar".
Usually used in the same context such as to say, "he's a fire-hearted bastard" or as response to someone who asks how your are doing. example:
"He walked up and slapped me on the back, then gripping me in a great hug. My father was always given to emotional outbursts that embarrassed me but I grinned anyway. It was good to see him.
When he asked how I was doing, all I could say in return was, "I'm fire-hearted and kicking, dad!"