I think because troll is originally a Norwegian word it makes it a little harder to decide exactly how it's pronounced, though I have heard "troll" to rhyme with "call" used, but when you look at internet trolls, they refer to them as rhyming with bowls, so I personally have always said the latter, and that's how my username is pronounced, and should be.
tl;dr: It's Trollheart to rhyme with stole heart, not Trollheart to rhyme with ball heart.
