Shadowfang keep is a wretched hive of scum and villainy, the product of betrayals and backstabbings, and is now "operated" by traitors, the undead, and their minions. The heroic version of this dungeon, suitable for level 85 characters with a minimum gear level of 329, has the same layout as the original, but the bosses are far more powerful. They hit hard and there are some things to be aware of when fighting them.
Before you get started you should make sure you have a few things.
Make sure your gear is repaired to 100% before stepping into the place.
Some healing potions will make life a bit easier on your healers. In some of these fights they will be pretty overworked as it is. A good one to get is the Mythical Healing Potion which restores about 20k health
Good food always helps, even if just a bit. Beer-Basted Crocolisk will give your 90 Strength and 90 Stamina for an hour.
Heirlooms are an interesting topic. Some of the heirloom items level to 85 (the other just go to 80) and so they have the stats to get into heroics, but they are item level 1. What this means is that the dungeon system might not let you in. You have to have an average gear item level (iLevel) of 329 and a couple of iLevel 1 items won't help that average. So send the heirlooms on and get other gear.
Heroics go a lot better if people leave the attitudes home. I've been pretty lucky and gotten into some great groups, but every once in awhile... Also, if you don't know something, then ask! The fights will go better and everyone will be happier. These are tough enough without fighting each other in addition to the opposition.
The bosses:
Baron Ashbury - He casts a lot of interruptable spells and you want to interrupt as many of these as you can. This fight will put a lot of pressure on the healers, so more interrupted spells means less pressure on them.
One of his abilities drops everyone to 1 HP (ouch.) He will then start a heal effect which heals you and the Baron. Zap that spell as quickly as you can afford to do so.
Towards the end of the fight he transforms into the Dark Baron and that's when you'll really want to pop your cooldowns and burn him down.
Baron Silverlaine - Summons a minor boss at three points during the fight. Your call as to whether to burn them down first of just work on SIlverlaine.
Commander Springvale - This guy is probably between the first two in difficulty, depending on your group. The commander will summon a pair of adds at various times during the fight. Lock them down, CC/interrupt them and otherwise keep them out of the fight. They aren't tough, but they greatly assist the commander and will make this a very long fight if you dont deal with them.
Lord Walden - His main power is chemistry. He will mix up a mystery potion and use it on you. You will get a debuff. If it's red, then stop moving, but otherwise do what you're doing. If it's green then keep moving (jumping counts as moving.) Then just burn him down.
Lord Godfrey - His main power is the Bullet Barrage he fires. Stay away from it (behind him if you can) and beat him down. He summons adds, but they aren't hard to deal with. His other big power is Cursed Bullet, which can be interrupted and hits very hard.
The Shadowfangkeep Heroic will keep you team paying attention. Like all the Cataclysm heroics it's hard and your group needs to be clued in to finish it. The better that your team can pull together and work together, the better of f you'll be. That said, leap in and have fun!