They key is what does declarer have for his 3NT bid? I'm thinking he just about has to have 14 hcp. including 5 ♦, so continuing ♥ is too likely to give him 9 or even 10 tricks. (5♦, 4 ♠, 1 ♥). So, I'm switching to the ♣ jack. Maybe partner has the ♣ K and a ♥ to return. If so, wonderful. If not, we're still alive if P has either the ♠ K, or, less likely, a slow ♦ winner. We' make 2 ♥ tricks, 2 ♣ tricks, plus P's winner, before declarer can come to 9. If declarer has faked me out with something like Kxx-Qx- AQxxx-Kxx, it wouldn't be the first time. And probably not the last, sad to say. :)