When performed, Fire Mario would spin around while surrounding himself with an electric shield. When performed on the ground, Fire Mario could not be moved, but when performed in the air, he could be moved slowly to the left or right while descending slowly. Opponents that would make contact with the shield would be dealt 10% damage and decent knockback. Additionally, if an opponent were to attack Fire Mario while using the Heat Shield, Fire Mario would then "parry" the attack by trapping the opponent in place and damaging them normally until the end of the move's duration.
It should be noted that using this move would actually extend Fire Mario's time limit, allowing the player to remain as Fire Mario for longer.