East should bid 4♣ . This agrees hearts and shows a singleton or void in clubs.
East South West North
pass pass 1♥ pass
4♣ 1 pass 4♦ 2 pass
4♥ 3 pass 4♠ 4 pass
5♣ 5 pass 6♥ pass
1 = agreeing hearts with a singleton or void in clubs (splinter bid)
2 = first round control of diamonds and slam interest
3 = nothing more to show
4 = first round control in spades and still has slam possibilities
5 = singleton ace or void in clubs
North starts with the ace of clubs, ruffed in dummy then crossing to the ace of diamonds to ruff another club followed by a diamond to the queen to ruff the third club. The king of trumps was cashed to find the bad break, so the king of diamonds was cashed for a spade discard, leaving this:-
There are two ways to play from here.
You can ruff the last diamond with the 6 of hearts risking an over-ruff, but it pays off and you can now cash two top spades and claim on a cross-ruff with top trumps.