Heitmann is someone who respects duelists with high potential and strong monsters and despises duelists with low potential and low monsters. He tried to expel Leo, Luna, Dexter, Bob, Patty and Sly due to their low performances. Yusei duels the teacher to make sure that the students wouldn't get expelled. Heitmann lost the Duel to Yusei by the same low monsters he despised.
In the dub, the Principal reveals that Heitmann only maintains his high position because his mother (whom he still lives with) is one of the Academy's principal sponsors.
Heitmann has an arrogant personality, looking down on those who use low level monsters, believing no matter how hard they try they cannot win with low level cards. His outlook starts to change though during his Duel with Yusei. He shows suprise when Yusei used a Tuner to draw 2 cards, and was shocked more when Yusei used a Tuner monster to Synchro Summon with a card from his hand. After being beaten by Yusei, he realizes the error of his ways and decides not to expell the students.
Heitmann uses a Deck based on "Ancient Gear". (In the dub, he calls it a "Vanguard Deck", but given his ego, he likely made that up.) According to him this is a vintage Deck that only Elite professors chosen by the Academy are allowed to use. Thus it is unknown if this is his real Deck or just a Deck used by all Head Instructors at the New Domino City Duel Academy.