Not quite sure how people bid to 4♥ but several did. South is too exposed to open 3♣ as the Clubs are not strong enough.

South could make a weak jump overcall of 3♣ when East opens 1♥ and then E/W might reach 4♥ 

However 4♥ should not make (although it did)

South has to lead the ♦ 7 (anything else gives a trick away) and North has to realise that with the ♦ J 10 in Dummy that the ♦ K Q 9 are 'equivalent' cards. Therefore North must just cover whatever Dummy plays. 

Now East has too few entries to set up and reach Dummy's Diamonds and the defence must come to two Diamonds, a Spade, and the ♥ K.

South has to resist the temptation to ruff a Diamond if she gets the chance. Her ♥ K will always make if she doesn't. If she does then she ruffs one of her partner's winners and no longer makes the ♥ K.