A difficult hand. 

West passes

North as a strong unbalanced hand with 4 losers (losing trick count) if a fit can be found, so opens 1♦ with the aim of rebidding ♥ s to show suit.

North will make things difficult by bidding 3♣ 

South should bid 3♠ to show suit and game values. Ax in ♣ s is probably not a good enough stop for NT (the case here)

North will bid 4♥ to show 5♥ s as South did not doule to show 4+♥ s, he must have 5♥ s and therefore 6+♦ s.

South has a choice - 5♦ or 6♦  4N would be RKCB for ♥ s, the problem of Easts ♣ preempt is a lack of space for the bidding.

Another interpretation of bidding ♦ and then ♥ s is that he must have a strong hand, otherwise he would have bid ♥ s and then ♦ . With this information 6♦  has a reasonable chance.