Hartman played Canadian junior hockey with the Belleville Bulls and North Bay Centennials of the Ontario Hockey League, where he compiled 102 points and 473 penalty minutes in 138 games. Hartman represented the United States at the 1987 World Junior Ice Hockey Championships and appeared for the Sabres later that same year, as he amassed six points in 17 National Hockey League (NHL) games. In 1994, he was originally left off the Stanley Cup along with teammate Ed Olczyk because they did not play the 41 regular season games or 1 game in the finals. Rangers protested saying Hartman and Olczyk had missed time due injuries, and should be on the Stanley Cup. NHL agreed and later added their names.