At trick 2 Declarer must lead his ♥A in order to unblock the ♥ suit. For as long as the Ace remains in his hand he can not play out Dummy's ♥K and ♥Q.

After winning the 2nd trick with his ♥A Declarer (at trick 3) then leads a small trump (♠4) from his hand to Dummy's ♠10.
If it wins the trick Dummy's ♥K and ♥Q can then be played, on which Declarer discards his two diamond losers (♦10 and ♦9).

If Opponents win the 3rd trick instead with their ♠A, Dummy's ♠K will provide the entry to Dummy when Declarer next gains the lead after which Dummy's two heart winners can be played.

Usually draw trumps first, but in some deals urgent action is required before drawing trumps (notably when the trump Ace is in Opponents' hands) to either

a. discard losers in one hand on winners in the other,

b. ruff in Dummy before Dummy's trumps have gone,

c. or (as in this case) unblock winners in Dummy's suits.