Watch them Spades

Q J 7 4
K Q 7 5
A 7 3
7 3
10 A 9 8 6 5
J 9 6 3 ------
K 9 8 5 Q J 5 2
A K 9 4 8 6 5 2
K 3 2
A 10 8 4 2
10 6
Q J 10

An interesting hand at three hearts, no? Do you think you'd make it? Can you make it, looking at all four hands if the defense is tip-top? West started with the A K of clubs and then shifted to the 10 of spades, which his partner let ride to the king. East did right to let that 10 ride. If he had gone up to give his partner a ruff, the hand is all over. Those are your four tricks. Good-bye.
After winning with the king of spades, declarer went to the king of hearts and found he had to lose a heart. He laid down the queen of spades, which East now took, and seeing his partner's void in spades, gave him a ruff. End of defense. Declarer can now draw trump with impunity and sluff a diamond on the jack of spades.

It was another case of a four-carders (well, this time East five-card spade suit, but the top four cards there). East rightly let the ten ride to the king, as noted above. He wants to get something with his ace besides his partner's ten, and he wants the 9 to protect the fourth round of the suit, inhibiting a discard of a diamond. That's his task. As for the ruffing potential, well, first you don't get anything with that ruff. Declarer isn't going to play the jack of spades on top of the ruff, is he? And if declarer abandons drawing trump after one round, you've got to suspect it's because he has a heart loser.
Well, if East led the 9 of spades to knock out the J, expecting to control the fourth round with the 8, isn't West at fault for ruffing with a natural trump trick? That's a valid enough point, of course. One can only point out that sometimes partners expect you to ruff on an opportunity they give you and West might have been too eager to please, and East could have led anything else. Still, I would place the major blame on West, myself. He knows he's always got that trump trick and he just might have ducked the lead. In any event, note that there are three cards the defense wants to get something with, to wit: the A of spades, the 9 of spades (or 8) and the J of hearts. Even if the 9 (or 8) is ruffed out and isn't a winner, as long as it's beating the fourth round of spades, it's getting something and that something is a diamond winner later.
The defense should have come to 2 clubs, a spade, a diamond and a trump.

Okay, let's say declarer played his hearts the other way, cashing the A of hearts and now sits with two honors over the J 9. But he still can't make the hand. He leads a low heart, as West splits his honors -- and now declarer has no quick re-entry to the closed hand and still can't make the hand.
If he leads a spade, East wins, of course. As above, he should be able to lead the 9 of spades, but fearful that his partner will spend a valuable trump on garbage, he shifts to a diamond, knocking out the ace. Now if declarer tries to get off dummy by losing a diamond, it is time to get that spade ruff without further ado, because declarer can pick up the whole heart suit if you let him and now the jack of spades is meaningless because he has nothing to sluff on it.

So declarer should never make this hand whether he plays the hearts t'other way or not. And basically it's a matter of controlling that fourth round of spades, getting something with your ace, inhibiting a fourth-round spade winner and sluff of a diamond -- until declarer has lost diamond control and can no longer use the fourth round of spades for anything.