S/EW		♠	K 7 3
		♥	J 10 6
		♦	6 4
		♣	10 8 6 3 2
				♠	Q 8 2
				♥	K Q 8 7 2
				♦	K Q 10
				♣	J 7

¹ North hopes to bluff EW out of their contract but is overdoing things...
² East has eaten too much pepper as well: vulnerable against not, on the two level on a shaky five card suit, instead of a healthy six card suit...
³ game forcing: 'tell me more'

West leads the ♥5 (third or fifth best) to the ♥10, the ♥Q and South's ♥A.
Declarer now plays the ♠A (West the ♠5) and next the ♠4 (West the ♠10) to dummy's ♠K. Next he plays a small club to his ♣Q, West winning with the ♣K. West returns the ♥9, declarer playing dummy's ♥6.
Which heart should East play and how should the defence continue?

Solution

First East should ask himself why, at the second trick declarer did not cross to the ♠K in order to finesse East's ♠Q? After all, declarer clearly started with ♠AJ964.
The answer can only be that the ♠K was dummy's only entry card. Declarer had to choose what to use it for:
1. To finesse the ♠Q, after which he could not finesse the ♣K anymore.
2. To finesse the ♣K, taking a considerable side chance of the ♠Q coming down.
Method 2 offers better chances because it 'combines' two chances.
Bad luck for declarer then, that both the ♣K was wrong ánd the ♠Q did not come down, while the finesse of the ♠Q would have succeeded.
Probably the contract will now be defeated, right? Well, it might, but it always pays to keep on thinking instead of leaning back.

West very probably started with three hearts: ♥954 (♥9543 is possible but unlikely; ♥94 is impossible, since he would have led the ♥9 then). So EW will be making this heart trick (but not another one). They have scored a club trick and East is bound to make the ♠Q.
The danger must be apparent to East: if declarer has one or two small clubs - next to the ♣A, he is sure to have - then the club suit has been established now. Declarer, who certainly has the ♦A as well, can pitch (a) diamond(s) on (a) club(s). Declarer has six cards in the minors. If he has 3-3, he can pitch his second and third diamond on dummy's fourth and fifth club. And if he has 2-4 in diamonds-clubs...

S/EW		♠	K 7 3
		♥	J 10 6
		♦	6 4
		♣	10 8 6 3 2
♠	10 5			♠	Q 8 2
♥	9 5 4			♥	K Q 8 7 2
♦	J 9 8 5 3 2			♦	K Q 10
♣	K 9			♣	J 7
		♠	A J 9 6 4
		♥	A 3
		♦	A 7
		♣	A Q 5 4

...he can pitch his second diamond on the fifth club.
EW are in a hurry therefore to establish a diamond: it must be cashable at the moment East ruffs a good club with the ♠Q.
East has a clear view of how the defence should be, West perhaps not. Therefore East does not take any chances: he overtakes West's ♥9 with the ♥K and returns the ♦K. This way dummy's ♥J becomes a master but that is unimportant. After all, declarer has no access to dummy - yet. He will win with the ♦A and cash the ♣Q but when he tries to cross to the ♣10, East ruffs and cashes the ♦Q, setting the contract.
(In the unlikely case West did start with ♥9543, South will ruff but then the contract was cold on West's ♥9 return: declarer concedes a trick to the ♠Q and makes two red aces and four tricks in each black suit).

Had East not overtaken West's ♥9, West would probably have found the diamond switch. 'Probably', not 'certainly'. So why should East put pressure to his partner if he (East) knows what should be done and can do it himself?
A good bridge player makes life easy for his partner!

PS: East of course must not cash the ♠Q (the master trump...) when gaining the lead with the ♥K...
PPS: Declarer missed an opportunity: if in trick one he plays the ♥6 in dummy rather than the ♥10, East probably will not have the nerve to play the ♥8. If East indeed plays an honour card, South wins and immediately plays back his second heart. Later, when in dummy by way of the ♠K, he discards his diamond loser on the good heart.
That would have taught East for overcalling too lightly (without the overcall South will certainly insert the ♥10 after a heart lead, hoping for West to have either the ♥Q or the ♥K).
West did not need East's heart overcall: without it he would have led a red suit anyway and South would probably have gone down, on the assumption he will handle the black suits like he did: logically but unluckily.