Both Vulnerable Dealer South.
Opening lead: 
2
South studied the hand before playing a high heart from dummy. The study, such as it was, didn’t work out the winning line of play. He led a trump at trick two. East ducked. South led a second trump. This time East rose with the ace and returned a trump to dummy.
South was now in a dilemma. He could take a simple diamond finesse, return to dummy with the queen of clubs, repeat the diamond finesse and score the slam. The alternate play would be to play four rounds of clubs to discard one of dummy’s diamonds and then take a ruffing finesse against the king.
South decided on the latter line because East had shown up with one more trump than West. The play lost and so did South.
South should have thought a little longer at trick one. Then he would have found a dummy reversal play to avoid any diamond problem. Here it is. Cash the second high heart, ruff a heart high, lead the deuce of trumps to dummy’s seven. The best defense Is for East to win and lead a trump back. South wins in dummy and ruffs dummy’s last heart high. Now he comes to dummy with the queen of clubs, plays out dummy’s last two trump and makes the last four tricks — the diamond ace and three top clubs.