What about on a Club lead?
* Trading on the favourable vulnerability.** Roman Key Card Blackwood, agreeing Diamonds.*** Two of the “five Aces” (where the King of Diamonds is an Ace); plus the Queen of Diamonds.§ There are no missing key cards, and North hopes his Hearts will set up.
Unwilling to expose partner’s Trumps with a singleton Trump lead, West tried the seven of Hearts. This appeared to mark