The other day I picked up the following hand: S K643 H 432 D Q7 C KJ42
My partner opened 1D, RHO passed and I responded 1S. My LHO also passed and my partner re-bid 3D, showing 6+ diamonds and a strong hand (16+). Obviously, we would like to be in 3NT but what is the best re-bid for responder with no heart stops? Partner has obviously denied 4 hearts as he would have reversed to show his strong hand instead of repeating diamonds. I actually bid 4D and partner went on to 5D, which did make, but a few tables at the club had found the 3NT game and got the better score.
Just bid 3NT. They haven't led a heart yet. Or you can play 3H as an asking bid in this sort of situation, but make a clear agreement on when this bid is natural and when it is not.
Another way to view your small doubleton in hearts is to look at it from the point of view of probability. Bridge is a game of probability. You have 9 points. Let's give partner 17 points, for argument's sake. That means that, of the 31 high card points held by the players other than you, your partner holds 17. The fewer points you have in a suit, the more room partner has for those points in his hand. You may have a small doubleton in hearts, but it's a reasonable bet that partner has points in hearts enough of the time that you want to bid 3NT in duplicate, or you'll get your tops when 3NT goes down and 5C or 5D makes, but you'll get bottoms when 3NT makes, and that will be quite often.