The ♦A is led (opponents lead Ace from Ace-King), East follows with the three. Plan the play after West switches to the ♣3 at trick two.

Solution:
If the ♠K is onside, the hand poses no major difficulties. Therefore, we should plan the play with the assumption that ♠K is with West, which is quite likely in light of the West's opening bid. The most intuitive play is to win the club return in hand, and play a low heart from hand, and eventually ruff two more hearts in dummy. However, when you give up a heart, East will win and return a diamond, forcing you to ruff. When you ruff a heart in dummy and take a spade finesse, if West plays the ♦K after winning the ♠K, you have to hope that the ♠10 will fall under your Ace, which is against the odds.

A better line is to win the club return in hand, and play the ♥K. This has the effect of making sure that West wins the trick, preventing them from forcing you in diamonds. Whenever hearts are 3-3 and spades are 3-2, you will make the contract.

On the given layout, i.e. when West holds the ace doubleton in hearts, playing the ♥K will fail. You can give yourself an extra chance by winning the club switch with the Ace in dummy at trick 2, and leading a low heart. If East plays a card lower than the 10, you will cover his card to ensure that West wins the trick. If East is awake and plays the 10 or a higher card, you have lost nothing, and will play the King in accordance with the earlier plan. When East holds four hearts and plays low, like on this hand, this effort of yours pays dividend.

Analysis:
Bridge Baron's double dummy solver confirms that the contract can be made by exiting with the ♥K at trick 3 whenever hearts are 3-3. The analysis also confirms that winning the second trick with the ♣A and leading a heart towards hand cannot lose, and has a chance of gaining.
Par Contract Analysis:
The par contract on this deal is 4♠ by North-South.

Bridge Baron deal No : N4565-95631-24042-59972-54048-80017