After 2 NT Opennings it is not possible to stop at 3 Diamonds level in any bidding system. In this convention developed by Jeremy Flint, 3 Clubs response to 2 NT opennings is used for transfer to Diamonds. Stayman is applied by bidding 3 Diamonds, and where 3 NT answer to Stayman means no 4 cards major, 3 Hearts response does not deny 4 cards of Spades. Since transfer to Hearts could not be done by bidding 3 Diamonds, at first transfer to Diamonds is done, then 3 Hearts is declared. Of Course if you intend to play 4 Hearts then you should bid 4 Hearts instead of 3 Hearts because the opener could not know your hand.