As a followup to my post with a few tips on Heroic Mechanar, here are some tips for Heroic Slave Pens.
Coilfang Defenders - These guys are immune to all forms of crowd control. However, they can be snared. They hit extremely hard, so it's best to kite one around (mages and hunters are the best choices) while killing the other.
Mennu - Pretty easy fight. Just make sure to kill all of his totems, except for the Corrupted Nova totem! It explodes when destroyed, so it's best to simply move the whole group away from it.
Rokmar - Very difficult in heroic mode. He's hard enough in regular mode! If you have just one healer, they should be doing nothing besides healing the main tank (unless they have some quick cast area or group heals). Running out of mana during this combat is definitely a possibility. Really just need to unload on him and the tank needs to work hard on maintaining aggro. He will very quickly tear through your party if he gets loose or the tank dies.
Quagmirran - Nature resistance certainly helps. And you want to get the buff from the imprisoned druid if you can, but the real kicker of this encounter is his acid breath attack. This is a frontal area attack, so you need to keep him facing away from the rest of the party. The only problem is that it also causes him to lose aggro on his target, which generally results in him turning around and spraying all the soft targets (or even worse, directly targeting one). So the tank will need to taunt, and the other players will need to use aggro-reducing abilities or just stop attacking for the duration of the breath attack. Improved taunt would probably help here as well.