Slamming the door too early

In standard methods, a jump to 4H is a sign-off. It shows a hand that believes that slam is not desirable and discourages opener from continuing the auction. 

That description, however, misrepresents North's strength. South has shown a strong hand with diamonds and hearts, so North's hand clearly has slam potential. Alternatively, a simple 3H raise would have been ideal for North. It is forcing, keeps the auction open, and gives the partnership space to cue-bid, show keycards, and reach the optimal slam. By jumping to 4H instead, North slammed the door too early, ending the auction without being able to explore slam. 

One way the auction could've proceeded is:1D - 1S; 2H - 3H; 3S - 5D; 5S - 5N; 6D - 7H.

In this sequence:

• 5D would be an exclusion keycard bid. 

• 5S would show one keycard, excluding diamonds

• 5NT asks for heart queen

• 6D showing the heart queen and diamond king

• 7H is likely North's final bid, knowing that South has additional values but couldn't describe them fully without bypassing 6H

This is only one possible auction. What matters most is maintaining a forcing, descriptive auction so that all the combined values can be accurately communicated. 7H has a great chance of making since it only needs hearts to be 3-2 (even 4-1 still has some chances).