South plays in 3NT and West leads the SK, East discarding a heart.

On this board communication between the hands will be a problem.

Declarer has 7 top tricks (1 spade, 3 hearts, 2 diamonds and 1 club), so needs to develop 2 more. If diamonds are 3-3, then there are 2 more tricks there, but 2 entries are needed - one to play the 3rd round and another to cash the established diamonds. Clubs could also yield 2 extra tricks, but this would probably involve losing 3 club tricks, or maybe more, and 4 entries are needed. 

Partly to preserve an entry to hand, Declarer must duck the first spade. West will switch, and Declarer retains 2 entries - a heart and a spade.

(It is interesting that this entry to hand cannot be dislodged by West without giving Declarer the contract.)

In the unlikely event that West switches to a club, it is best for Declarer to duck, hoping for a continuation, which should lead to 2 extra tricks being established.

However, West is more likely to switch to a heart or diamond, and it is best now to try for a 3-3 diamond split. Even if diamonds are 4-2, there might be chances for Declarer to make 9 tricks.

Declarer plays DA, DK, HQ, HK, D7. Declarer now is cut off from the CA. But this is not really a problem. On the actual hand West has to return a club or a spade, either giving the 9th trick. But even with East having the DQ, and a different distribution of the hearts, it will normally be possible to throw West in to lead a spade or a club, without losing more than 4 tricks in total.