Vulnerable: Both, Dealer: South
Opening lead: 
Q
Successful defense requires fast thinking. In particular a defender must use the bidding to picture the strength of declarer’s hand. This information, plus that gained from partner’s opening lead, should help a defender be ready with the right plays. Look at today’s deal from the point of view of East.
After the no-trump opening and the two-club inquiry for a major suit, South became declarer at four hearts. The opening lead was the diamond queen. If South held only a 15-point no-trump opening, that would give West five high-card points, and East could see that three of those would be the Q-J of diamonds. At best West could hold another queen.
East could see a heart trick, only one club trick, and the ace of spades coming to the defense, but that would not be enough to set the contract. The defenders would also need to make a diamond trick. Knowing this, an astute defender will decide early in the hand not to rush to grab the ace of spades when declarer leads the lone spade from dummy.
Declarer should win dummy’s diamond king and play a spade at trick two. If East ducks without apparent thought, most likely declarer will misguess and put in the spade jack. Now a second diamond play will beat the contract. Obviously it does no good for East to be caught napping and to trance before following with a low spade.
It would also be a reprehensible violation of the proprieties of bridge for East, if he held Q-8-6-5-3 of spades, to hesitate even slightly on the play of the spade from dummy, as though he might be ducking with the ace.