[shnk]

I love negative doubles when opponent overcalls hearts: I get to show exactly 4 spades or definitely 5+. When they overcall spades, I get confused when I have a 5+ card heart suit whether to double or bid hearts.

1)
1♦ - 2♠ - X - P
3♦ - P - 3♥

2)
1♦ - 2♠ - 3♥

What's the difference in terms of strength and heart length?

[helene_t]

The second auction shows 5+ hearts and is forcing to game. Since it is forcing it doesn't have to promise more than five hearts.

The first one shows long hearts but a hand that is too weak for an initial 3♥ bid. It still shows some interest in game, opener is allowed to raise to 4♥ if he has a suitable hand. Since it is nonforcing opener should be able to pass with a singleton hearts, so it should show at least six hearts.