We know, we know. You would have led the ace of diamonds and given partner a diamond ruff. But youre a great player and these were only experts.
South won the opening heart lead with the ace and ruffed a heart in dummy. He then cashed the ace of clubs and ruffed a club, followed by cashing the ace of spades. Declarer then led the diamond king to Wests ace, and West returned a diamond to Souths queen.
South exited with a low spade to West, who played his last safe exit card, a club. South ruffed the club, cashed the king of spades, and led a spade to West.
West, down to only diamonds, had to put dummy on play and allow South to enjoy the established diamonds. Making four after a well-played hand.
Its possible that a different North would panic after the double and bid four no trump for the minors, leading to a five-diamond contract by South. Oddly, it would also take a diamond lead to defeat that contract. On a heart lead, South would win, lead club to the ace, and ruff a club in his hand. A heart ruff back to dummy would allow another club ruff.
South would ruff another heart in dummy and lead the jack of diamonds. West, with nothing left except spades and diamonds, would eventually be forced to win his second diamond trick and lead a spade into dummys ace-king-jack. We know, we know. You would have led a diamond against this contract also.