This is close IMO. I'm not putting villain an an ace here to be honest. I'm putting him on Tx, JJ or QQ. Given that, I like this river bluff. I think the K along with unlikely hearts gives you just enough equity.

I'm just not feeling Ax here. I think Ax very often makes a small value bet into you on that river, since the K is likely to have hit you if you missed the ace. This is a bet I would make in certain specific spots.

Your decision rests solely on how loose and or passive the villain is with his range. I think if he folds Ax to that river bet sometimes, the bluff is an obvious +EV move given the lines.