This deal is from an EBU duplicate in December.
Two problems to solve here, the second one is more difficult than the first.
1) How does South make three hearts on a trump lead?
2) How does the defence beat three hearts?
To make three hearts on a trump lead, win the trump in hand and play a spade. West has to win and plays another trump, win this with the queen in dummy and trump a spade. Now play a club, again West must win and can only play two more rounds of clubs which you ruff in dummy. Now trump another spade, setting up the queen of spades as a winner and lead a diamond towards the queen.
To beat three hearts West must start with three rounds of clubs, this takes an entry out of the North hand before declarer has had a chance to play a spade towards the queen.