It can Proc. and Stack with the Normal version of this item. Equipping both Normal and Heroic will provide a total of 318 Spell Power and 272 Mana Per 5 Sec. (When mana regeneration buff is up).
The Mana Regeneration Buff is called "Energized" and will activate each time the player casts a spell, no matters if it is an offensive, defensive or utility spell, every type of spell will activate the Buff.