Here is a common type of deal with a position in Hearts that we have noted  many times before.

East-West reach 3NT in rapid fashion and you are on lead with a five-card suit. You duly lead your fourth highest Heart and partner produces the ♥J, which forces the ♥A. You can be confident  that your partner has the ♥Q as East wouldn’t waste his ♥A on the lowly ♥J had he started with the ♥A Q.

Note, in passing, that declarer cannot afford to duck a round or two of Hearts. From declarer’s perspective it makes no sense to break North-South’s communications in Hearts as he must take the Club finesse into your hand (so running North out of Hearts is simply pointless). The best chance for 3NT is to grab the ♥A, cross to table and run the ♣J. This way 3NT makes if the Club finesse works or if Hearts are 4-4 – and you have led the ♥3 so the chances are good that Hearts split. Ducking a Heart is risky as a Spade shift will beat the hand if the Club finesse fails.

So, declarer takes the ♥A, crosses to a Diamond and runs the ♣J, hoping for good things. As South you can take this trick and can continue with Hearts, safe in the knowledge that North has the ♥Q.

One cloud may darken your horizon. Suppose North started life with just two Hearts, the ♥Q J alone. Now a low Heart at trick four would block the Hearts as North would take the ♥Q and would have no Heart to play back to your ♥K 10 7.

Well, if that were the layout then there is nothing that could be done. East would have ♥A 9 6 5 and there would be no way of unblocking the suit for the defenders. You might think of cashing the ♥K (dropping the ♥Q) and follow with the ♥10 but East would have the master ♥9 now and enough tricks for his contract.

The only chance of beating 3NT is that North has three (or even four) Hearts – with that in mind you should continue with a low Heart to partner’s Queen. As the cards lie you have four Hearts and the ♣K. 

One down.

Too easy? Maybe, and then again...