Usually when the flop is monotone you're not up against a flush. Slightly less than a quarter of the suited hands in his range will be hearts and suited hands are usually about a third of his range. So that's less than 1/12 of his range being on a flush. And out of about 2/3 of villains range being offsuit, less than half will have a heart. So that's slightly less than 1/3 of his range being on a flush draw.
So is villain a passive player? Or would he semi
bluff raise you in this spot? If he's a passive player just fold because he's probably got the flush.
OTOH If he would always semi bluff and always bet a flush and never bet anything else I would figure about a 20% chance he's on a flush and a 80% chance he's on a flush draw. The flush draw has a 36% chance, so overall that's a 49% of him getting a flush by the river. But you have about a 30% chance of improving to a boat. IOW I would figure I have about a 60% equity at this point.
And when you shove you have some fold equity. If he was semi
bluffing he has 36% chance of improving. So if your shove is less than 1.28 times the pot you can figure he will call and with 60% equity its favorable for you. If your shove is more than that he should call with the flush or otherwise fold. If he has the flush 20% of the time then up to 4 times the pot is favorable for you.
But a better approach, I think, is just to call here. The reason is you get to see another card. If its a heart you can shut down. Otherwise if he had semi bluffed his equity is down now down to 18% and he'll probably check to get a free card. When he does that you can raise. If he does bet again you should fold, unless you think he's a maniac.