I won't discuss whether or not you should macro Heroic Strike or not cause that's already sufficiently covered in this topic. However, I will correct your macro syntax.
Originally Posted by Sirloinsteak
You should never include the rank of the ability if you intend on always using the maximum rank. It will default to the maximum rank your character knows. Only if you require to down rank your ability would you use an explicit rank, and the only real use for downranking in the game currently is for a warlock using Life Tap(Rank 1) to charge a trinket before a pull without burning a large quanity of health.
/cast Heroic Strike
Additionally, when Cataclysm is eventually released, macros with references to ranks will likely cease to function as all ability ranks are being removed and rather the abilities will scale with level naturally.
In regard to the #showtooltip syntax, this will always default to the first ability in the macro the current modifiers would trigger. Since you want it to show Devastate and that is the first ability in the macro you don't require explictly defining which tooltip to show.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.