You can transfer Pokemon, but you can't trade.
Since HeartGold was released before Black, HeartGold doesn't know Black exists.
However, Black knows HeartGold exists.
You need to be on Route 16 in Black version, which requires beating the Elite Four.
After beating the story and obtaining the National Pokedex. Go to Route 15 in Pokemon Black to the Pokemon Shifter Building. Connect a second DS running Heartgold. There you will be able to transfer up to 6 Pokemon from Heartgold to Black/White. Make sure the Pokemon transfering have no items and do not know HM moves(Cut, Surf, Flash, ect) You can not trade or transfer from Black/White back to Heartgold.
No, but you can trade Pokemon only in HeartGold to Black
you can trade pokemon from heartgold to black but you can only transfer the pokemon in heartgold not trade it from black
Yes.
No, because Pokemon Yellow is only able to connect to Pokemon Red and Blue. I think Silver and Gold, too. Pokemon HeartGold can only connect to the DS Pokemon games. Besides the migration from Gameboy Advance.
you can transfer it from Pokemon soulsilver/heartgold to Pokemon black
yes, you can connect with HeartGold.
No they can't.
Yes you can. You can also do that with Pearl, Soulsilver, and Heartgold.
Not directly. You have to migrate to diamond pearl platinum heartgold or soulsilver first and then after you beat the elite 4 in white you can connect 2 da systems to migrate from diamond pearl platinum heartgold or soulsilver over to Pokemon black or white.
Yup, Pokemon diamond and pearl can connect! Even platinum and Heartgold soulsilver! Its like crazy!
You cannot transfer pokemon from HeartGold to Black until after you finish the main part of Black. Do note that you will be transferring pokemon from HeartGold to Black, not trading pokemon between the games.