What is the point of beating Heroic mode for any adventure?

So I recently bought the League of Explorers as one of my first paid items in Hearthstone. I loved it, and how interesting all the cards were.

Now after I beat the default bosses, a new mode showed up named 'Heroic'. When reading the description the only thing different from normal mode is "Heroic mode is NOT for the faint of heart!", and within the section itself there was no treasure chest icons like in Normal.

What is the meaning of doing Heroic mode? It seems beating it should give you the golden version of the card normally unlocked but there is no text describing what you get.