4♥ is a game bid. In most circumstances, it is a sign off.
As an opening
A 4♥ opening is to play and may be preemptive.
After a ♥ opening
After a notrump opening
- 4♥ after a notrump opening is a Texas transfer to 4♠. It shows 6+ hearts and game-going values.
After a 1♠ opening
- 1♠--4♥ is a double jump shift and is typically used as a splinter bid. This shows game-forcing 4+ trump support for opener's spade suit and a singleton or void in hearts.