I actually look at this hand a slightly different way. I don't see a polarized situation here (meaning he either has the flush or air). There's not really a lot of air here that makes sense besides gutters, and he'd have to call twice and then bluff - at a small sizing - which is a lot of unlikely things that need to go right for him to have bluffs here.
That being side, with this small sizing, it's not impossible that we see some worse Ax here trying to block bet the river when the third heart comes in because they are afraid of facing a larger bet.
Now with this EXACT sizing, I do sort of expect we run into flushes more often than not, and I'd certainly rather have a heart in my hand to block some flush possibilities. But that's based mostly on experience. And my experience ALSO says that we see some of that Ax and very occasionally some random stuff here that just doesn't make sense.
I'd be very on the fence in game based on the above, but I'd probably lean very slightly toward calling. Definitely calling if I have the Kh in my hand.