I agree that 3H asks for a heart stopper. Yes, I have one. I would bid 3N. So, if there is any further bidding by the cue bidder, it shows interest in a diamond slam and asks partner to cue bid controls up the line. Some might play Minorwood (RKC) by bidding 4D. In the auction, 1D, 1N, 2H, 3H, p 3N, 4D. It says "partner, diamonds are trump." With no knowledge of partner's diamond holding, the original diamond bidder would have a long solid diamond suit and a powerful playing hand in diamonds becausse with minimum values, he would be happy in 3N. Also, if over 3N, partner bids a different suit other than diamonds, those bids would still be controls with diamonds set as the trump suit. Partner is asked to bid Aces, and even Kings, up the line. This allows the partnership to stop in 4N when there are not enough controls for slam.
