Neither side vulnerable.  
South deals.
                              NORTH
                              S: K 6 5            
                              H: K 6 2       
                              D: A Q 9 4 2   
                              C: K 8     
            WEST                             EAST
            S: 7 4                           S: J 9 3        
            H: Q 9 7 3                       H: A J 5      
            D: K J                           D: 10 8 7 3          
            C: A Q 6 5 2                     C: J 9 7       
                              SOUTH                         
                              S: A Q 10 8 2 
                              H: 10 8 4     
                              D: 6 5       
                              C: 10 4 3   
                  SOUTH    WEST    NORTH    EAST                  
                   Pass     1C     Double   Pass
                    2S     Pass     3D      Pass
                    3S     Pass     4S      All Pass

     The opening lead is the three of hearts.  Before reading
further, decide if you would prefer to declare or defend.
     It looks as if there are only nine tricks available for the
declarer.  The combined holding of the North and South hands is
only twenty-one high card points and a couple of doubletons. 
South's two spade bid seems fairly aggressive, as does North's
three diamond call.  Given all of this, you should choose to
defend.  But be careful.  To beat this hand, you are going to
have to defend well.  Look at what happened at the table after
West led the three of hearts.
     Declarer played a low heart from dummy and East played the
jack, which won the trick.  East switched to the seven of clubs. 
South played low and West won the ace.  It is trick three and
West is at the critical juncture of the hand.  Unfortunately, he
selected the queen of hearts as his next lead and Declarer
covered with the king from dummy.  East won the ace, establishing
the ten of hearts in the South hand as the tenth trick.
     What if the defenders avoid the heart suit all together? 
Let's make West lead the four of spades.  This goes to the ten in
the South hand.  A diamond is led and the queen covers the jack
and wins the trick.  The ace of diamonds is cashed and a low
diamond is ruffed with the eight of spades.  A club is led.  West
wins the ace and continues with a club (a trump is no better). 
The king wins this trick and declarer ruffs another diamond with
the queen of spades.  South leads his last club and ruffs in
dummy.  The king of spades is cashed and the nine of diamonds is
led.  This is the end position:                               
                              NORTH
                              S: V o i d          
                              H: K 6 2       
                              D: 9           
                              C: V o i d 
            WEST                             EAST
            S: V o i d                       S: J            
            H: Q 9 7                         H: A J 5      
            D: V o i d                       D: V o i d           
            C: Q                             C: V o i d     
                              SOUTH                         
                              S: A          
                              H: 10 8 4     
                              D: V o i d   
                              C: V o i d
     East may ruff in which case South pitches a heart and East
is endplayed, or East may pitch, in which case the nine of
diamonds becomes the tenth trick.
     In spite of this you should elect to defend.  East must lead
one round of hearts and one round only.  When he regains the lead
with the ace of clubs, he must lead another club.  The defense
will now score the ace of clubs and three heart tricks or two
heart tricks and a trump, depending on how declarer continues.  
---------------------------------------------------------------------