What gym do you go to after beat misty in heart gold?

You don't go to a gym after beating Misty in HeartGold. After defeating Misty at the Cerulean City Gym, you continue your journey towards Route 4.

Here's what happens next:

* Route 4: You'll encounter trainers and wild Pokemon, and you might find a TM for Flash.

* Route 5: You'll meet Bill and help him with his Pokemon before continuing to Violet City.

* Violet City: You'll face the next gym leader, Falkner.

So, while you might be thinking of a specific gym after Misty, the journey continues on, with more challenges and exciting encounters ahead.