They don't. If you read Heroic it starts with: "Whenever you cast a spell that targets....". Abilities aren't spells. You'll need to cast an instant, sorcery, or aura (usually) to trigger Heroic.
May 24, 2014 5:48 p.m.
No abilities do not trigger heroic and for an example of why imagine a modern game with T1: 1 drop, T2: Phalanx Leader , T3: Outrider en-Kor targeting Phalanx Leader 1,000,00 times with the 0 mana ability. Swinging with two 1,000,000/1,000,000 on turn 3 is silly