Irelia dashes to an enemy, dealing 5 / 25 / 45 / 65 / 85 (+0.6 per attack damage) physical damage and restoring 9 / 10 / 11 / 12 / 13% of the attack damage as health to herself. If the enemy dies or was unsteady, the cooldown is refreshed. Deals 55−259 bonus damage to minions (depending on level).
This gives you some massive burst. With a Bloodthirster (fully stacked) & Trinity Force (these two are a very good combo by the way), ~900 damage with this combo. Pretty good burst to scare off an opponent.