Both sides vulnerable.  
East deals.
                              North
                              S: A 10             
                              H: 10 6 3      
                              D: 9 7 5 3     
                              C: J 7 6 3 
            West                             East
            S: 6 5                           S: 7 4 3 2      
            H: Q J                           H: 4          
            D: K Q 6 2                       D: A 10 8 4          
            C: A K 8 5 4                     C: Q 10 9 2    
                              South                         
                              S: K Q J 9 8
                              H: A K 9 8 7 5 2
                              D: J         
                              C: Void     
          The Bidding:  
                   East   South     West   North                  
                   Pass    1H        2C     Pass
                   Pass    2S       Pass    3H  
                   Pass    4C       Pass    4S  
                   Pass    6H    (All Pass)     
          Opening lead: KC
     There will be many who would advocate a two club opening bid
with the South cards.  I do not agree.  With only fourteen high
card points, there are plenty of points in the other hands to 
keep the bidding open.  Additionally, it is very difficult to
describe a two suiter when you have opened at the two level.
     After the one heart opening, West makes a normal overcall
and North passes.  East may think of raising clubs but both sides
are vulnerable and he can always bid later if he gets the chance.
     South now bids two spades.  Is this a reverse bid?  The
answer is: Yes and No.  To really be a "reverse" South would have
to bypass one no trump and bid a suit that is at a higher level
than the first bid.  The only thing here is that the suit is
above the initial suit, hearts.  So this is absolutely forcing
and should show a very good hand.
     North shows a preference for hearts and South now shows slam
interest by bidding four clubs.  When a partnership has agreed on
a suit, a cue bid asks for additional information from the other
side of the table.  If North held the ace of diaomds he would bid
four diamonds.  If North had no aces or voids he would just sign
off at four hearts.  Even though it seems strange, North must
participate and show the ace of spades.  
     South has all the information he needs and just bids six
hearts.  It is not a 100% slam.  Hearts have to break - but the
odds favor a 2-1 division.  All is as it should be and twelve
tricks are easy.
     This is a difficult slam to bid - without North's excellent
four spade cue bid the final contract would be four hearts making
six.  Work on these cue bidding situations with your partner to
help improve your game.