You cannot rely on Blackwood or Cue bidding first round controls to give you all the information that you would like to bid a slam

With this deal East enquires for first round controls from West and finds out that one Key card (presumably an ace)  is missing. You can sign off in 5H or think some more.

It is clear that West has a powerful hand but taking into consideration your heart holding there must be much more to West’s hand if he/she hopes to win 10 tricks. You can account for 10 spade cards so there is a reasonable chance that West is void in spades: if that is the case then West must hold both minor sui Aces assuming that the 5C response showed 3 controls; an almost certain probability. There must be a good chance for a slam, and there is the added consideration that as East you have an opening hand with excellent trump support. Therefore bid 6H

¹ Key card Blackwood

² 0 or 3 Key cards

Results

4HW +2 (twice); 4HW +3 (twice; 5HW +1, 6HW +1

 N-S 1^st   J Faulkner & A Ridderhof….62.1.0 % 

         2^nd W Jurgensen & G Ford……56.4%

 E-W 1st H Clohessy & R Orford…….67.1%

          2^nd Dianne & David Long……..52.5%