Matchpoints. Some spots might have been wrong but the relevant ones are correct.
Partner leads the 3♣, to the J, Q, and A.
Declarer cashes AK♥, then leads a heart to partner's Q. (Partner also had J♥ if it matters.)
Declarer is not an expert.
What do you signal?
If it matters you're playing UDCA, but there's probably something reasonably equivalent no matter what you're playing.
(I was West. East tanked. We ended up getting it wrong (possibly my fault) in a way that only good players could but still got a top.)