On the way to 6*H*, you asked for aces via 4NT. West leads the *H*5, which you win in hand. Both follow to a second heart. Plan the play.
The idea is to try to avoid the diamond guess if possible. Draw a third round of trumps, discarding a club from dummy. Your next move should be to cash the dummy’s three top spades, discarding two clubs. Ruff a spade and exit with the *C*K.
If West has the *C*A and no more spades, he will be forced to lead a minor-suit card, ending the play. If West gets out with a club, a club winner will be established for a diamond discard. If West gets out with a diamond, you can claim. If West has a fifth spade and leads it, ruff and try to get the diamonds right. The idea is to try to figure out which opponent has more diamonds and play that person for the queen. If West started with five spades, East is more likely to have diamond length.
If East has the *C*A and doesn’t have a spade to lead, East’s best return is a low club, which you should ruff. If West started with a doubled *C*Q, you won’t have to guess the diamonds, otherwise you will. If East has a spade to lead, it’s basically back to the diamond finesse. You have given yourself your best chance to avoid the diamond finesse. The full deal: