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

pass        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.