Trick 8		North > 4♥
Declarer (W) ♠ - A 10 9 8 6 ♥ - A 10 5 ♦ - A K 3 ♣ - A 3	A♥ w		3♥	Dummy (E) ♠ - K Q J 7 3 ♥ - K J 3 ♦ - Q J 10 ♣ - 9 2
		Q♥ South		Won = 7 Lost = 1

If North (at trick 8) leads a ♥, Dummy plays low, and Declarer catches whatever South plays to the trick.
If South plays low too, Declarer wins with his 10♥.
If South plays the Q♥, Declarer catches it with his A♥ and Dummy's J♥ will now be the third ♥ winner.  

In fact Declarer gets a free finesse in hearts which can not fail to win. Next ?