If you want to know how to beat Heroic Karazhan Julianne the Opera Wing then the video, deck list and notes in this post will take you through it and make it really easy for you.
By completing Julianne on normal mode you unlock the following cards:
To beat Julianne on Heroic one of the best decks is a Reno Paladin deck (full list below). As long as Romulo is on the board Julianne is invincible, so you need to take him out to deal damage to her.
Board control is important, being able to overwhelm her and keep sticky minions on board to keep the damage coming in each turn is the way to win as you will see in the video below.
How to Beat Heroic Karazhan Julianne the Opera Wing
Deck List for Heroic Karazhan Julianne the Opera Wing
Paladin Class Cards
Muster for Battle
Keeper of Uldaman
Lay on Hands
Spawn of N’Zoth