Opening lead: K (king from ace-king in supported suits). The bidding can go several different ways after South’s 4 bid. West might be tempted to bid 4, which looks like a reasonable sacrifice against 4 – if 4 can be made. But guess what, it can’t!
On the other hand, if West does bid 4, it might provoke East-West to bid 5 which is down two!
North’s double is negative, showing at least four hearts with 8+ HCP but is unlimited when holding four hearts. South assumes the minimum count for the time being. East’s jump to 3 is preemptive. With cuebids available to show stronger supporting hands, jump raises are considered weak and preemptive. Important.
West leads the K and East signals with the queen to show the jack. It is a neat signal, allowing partner to safely underlead the ace if necessary. On this deal, it is necessary.
West shifts to his singleton diamond and, when in with the A, underleads the A to partner’s jack to get a diamond ruff.
If East wishes to continue this session with his partner he had better return a diamond! With something like Q 9 x x, East should play the 9, attitude showing the queen, making the underlead a piece of cake.