Checking when the 3rd heart falls screams "I'm scared of the flush", which basically (In most cases anyway) turns your cards face up. And you give villian a chance to take over the hand. I'll often bet here with air if I get the read that my opponent hates this card and isn't normally a tricky player who will "pretend" to hate the flush when in fact he hit it.

And it never fails if I give the oppenent a free card a 4th heart will fall and turn my hand to shit.

So I say b/f is the way to go at this level anyway. Checking does nothing to help you and leads to even harder decisions.