Whenever you see a solid suit in dummy without the ace and there’s no obvious side suit entry, the “alarm clock” should sound for both you and partner.
If you don’t hold the ace of that solid suit, you must give honest count in the suit being led.
If you do hold the ace, you must be able to rely on partner to give count.
So firstly West should duck the first heart trick and wait for East to show count.
When East plays ♥ 2 you know partner has a 3 card suit. It can’t be a singleton heart because declarer would have supported hearts holding 4 hearts, and East can’t hold 5 hearts because declarer wouldn’t have opened 2 NT with a void.
YOU NOW KNOW THAT DECLARER HAS EXACTLY 2 HEARTS.
YOUR PLAN SHOULD BE TO HOP UP WITH YOUR ♥ A ON THE SECOND ROUND OF THE SUIT TO MAKE IT IMPOSSIBLE FOR DECLARER TO ENJOY ANY MORE TRICKS IN THE HEART SUIT.