Every 18 seconds, Varian's next Basic Attack deals 144.9 (+3.5% per level) bonus Spell damage. Basic Attacks reduce this cooldown by 2 seconds.
Patch changes
(Patch June 13, 2017) Note: The Quick Cast setting for Varian’s passive Heroic Strike Trait has been removed from the Quick Cast Settings menu.
(Patch December 6, 2016) Note: Bonus damage changed from Physical to Spell; No longer heals from Second Wind, and now benefits from Ability Power.