I think that your smart move is to call down this hand. If he really is as much a maniac as you say, he could have any number of hands that you have beat. Ah and anything, KQJ of hearts, maybe with a 7 or 8. Maybe he has 66 with a heart. Maybe he has a made flush, or a pair of tens, but based on your description, the odds are just as good he could be betting a ton of hands you're behind. Even if he has a hand you are behind, you still have outs, and a J or 6 of hearts could easily win you a huge pot if he does have a flush or a flush draw (especially the nut flush draw). So, I think when you range in all of these factors, it is +EV to stay in the pot.

I favor a call here rather than a raise. Given that you just aren't sure where you stand in this pot, I'd take the river card assuming that you can probably get a bunch of money in if you improve. If you're behind now against a maniac, a raise on the turn could trigger a reraise that would give you an uncomfortable decision.

You don't want to fold, because this opponent has way too many hands you could be beating here. Raising opens you up to having to make a very tough decision when you won't really be sure where you stand. Seeing the river has value here, as you have the chance to improve to a hand that get all your opponent's money in the pot with the absolute nuts.

I suppose if I was sure the villian wouldn't come back over the top of my raise, I'd lean towards a raise, but against a maniac like this one, I don't think you can be at all sure.