Test Your Play

The idea is to make the contract even if East has the ♣K. Start by playing three rounds of hearts.
If East ruffs the third heart (unlikely), you’re a goner no matter who has the ♣K. If you overruff and throw East in with a spade forcing a club return, you’ll have only 11 tricks: four spades, four hearts, two clubs and one diamond. Discarding a diamond is no better as East can exit a spade if he has the ♣K or exit a club, driving out dummy’s ♣A, if he doesn’t.
If East has exactly three hearts, stop playing hearts. Lead a spade to the 10, cash two more spades and throw East in with a spade. The forced club return (assuming West started with
seven diamonds for his three-level preempt) gives you 12 tricks: four spades, five hearts, two clubs and one diamond.
If East has four hearts, cash four hearts before throwing him in with a spade. The idea is to strip East of hearts before throwing him in with a spade. You cannot allow East to ruff a
winning heart. Period.
East has a chance to make a clever defensive play. If East plays the ♥10 convincingly enough on the first or second round of hearts and cons you into believing that he has a doubleton heart, and you stop playing hearts to take the spade finesse followed by a spade throw-in, you will not be a happy camper when East exits a heart, rather than the hoped-for club.
Thanks to Tim Bourke of Australia for this one.

After winning the ♥K, cash three clubs and three spades, overtaking your second spade, and cash three more clubs, reducing all hands to three cards. Dummy has two spades and a diamond, and you must reduce to the blank ♥ A and the ♦K J. If the spades have divided 3–3, take dummy’s two winning spades and concede a diamond. If spades were 4–2, lead a diamond. If East has the long spade, you need to find West with the ♦A to make the contract, so stick in the jack. If West has the long spade, you need to find East with the ♦A, so rise with the ♦K.