Since this is 2/1, don't ever, ever, ever rebid 3♦ as that is an invitational, non-forcing bid. My bid is 3♠, a splinter and slam invitational. It confirms a heart fit and implies ♦ values. Partner is invited to show first round ♦ control at the 4 level (100% forcing). I have sympathy for 3♣, a cue bid, as partner can now show a ♦ stopper with 3♦ (forcing, because once responder starts a cue bidding sequence, all bids are forcing below game). 3♣ cannot be a second suit or game try in this sequence, except by prior agreement, because once an 8+ fit is found modern practice requires responder to bid game with an unappealing minimum (a flat 12-13 HCP) or investigate slam. Here, 1♦ - 1♥ - 2♥ - 3♣ - 3♦ - 3♠ would guarantee the A♣, A♦ or K♦, and second round control in spades.