South’s four-heart bid was a slam try, raising himself to four spades and showing the ace of hearts on the way. It was an aggressive choice with his hand but would have been about right if you added the jack of spades to his collection. Was it too aggressive? Not if he could take 12 tricks!
South won the opening heart lead with his ace and led a low club to dummy’s queen, West ducking of course. He then ran off five trump tricks and both high diamonds, leaving this position:
Declarer led his last spade and West was helpless. Should he discard a heart, dummy would part with a club and take two more tricks with hearts. A club discard by West instead would see a low heart discard from dummy. South would lead a low club from his hand to set up his king. Very well played!