Both sides vulnerable.  
South deals.
                              North
                              S: A 10 9 6 4 2     
                              H: 4           
                              D: A 6 5 4 3   
                              C: J       
            West                             East
            S: 8                             S: 5            
            H: K Q 10 9 5                    H: J 8 7 3 2  
            D: 8 7 2                         D: J 10              
            C: Q 8 7 5                       C: A K 10 6 3  
                              South                         
                              S: K Q J 7 3
                              H: A 6        
                              D: K Q 9     
                              C: 9 4 2    
          The Bidding:  
                  South    West    North    East                  
                   1S       2H      3H       4H 
                   Pass    Pass     4NT      5C 
                   Pass    Pass     6S  (All Pass)
          Opening lead: HK
     I found this hand to be very interesting.  I was playing
with Mort Pierce of Chagrin Falls in a matchpoint duplicate game. 
Pierce made one bid on this hand and became the declarer at six
spades.
     I held the North cards and when West made a two heart
overcall I had an easy three heart bid.  East bid four hearts and
Pierce has no reason to do anything at this point.  I bid old
fashioned Blackwood and East decided to get his second suit in. 
This was actually good to hear.  If East and West had the "stuff"
in hearts and clubs, then is was pretty likely that Pierce had
some points in diamonds, which would be good for our side.
     We play DOPI when the opponents interfer with our Blackwood
auction.  A double by Pierce would show no aces while a Pass
shows one ace.  The next suit bid would show two aces.  
     Knowing that partner held an ace made it hard to imagine a
hand where he could not make twelve tricks.  Also, when you are
playing matchpoints you can be a little more aggressive on hands
like this.  It is not like team events or rubber bridge where you
may want to be more careful about going minus when a vulnerable 
game will be easily made.  At matchpoints it is just one board - 
no more and no less - so I did what felt right and bid the small 
slam.
     As you can see twelve tricks was pretty easy.  Afterwards,
East said that he should have bid seven hearts.  It would only be
down four for minus 1,100 instead of 1,430.  I looked at the
recap sheet after the game to see how that would have affected
the outcome and I was surprised to find out that Pierce and I
were the only pair to bid this slam.  All of the other tables
were in four spades making six or seven.  So the well thought out
seven heart bid would have received the exact same matchpoint
result.  How about that?