Heroic Strike is a core warrior ability learned at level one. An instant strike, it is meant as a rage dump for when the warrior has ample amounts of rage to spend. Using a one-handed weapon will result in more damage.
As the warrior's first ability, this ability is used constantly during the first few levels, mostly because there are few other options for spending rage.
Heroic Strike costs 30 rage, and a successful Heroic Strike attack does not generate rage. As a result, the actual cost of Heroic Strike is 30 rage + the rage that would have been generated on a successful auto-attack.
When tanking, this ability is not as useful as [Devastate] or [Sunder Armor] due to its lower natural threat value, its removal of rage generation from normal attacks, and being tied to the weapon's swing timer. However, burning extra rage on Heroic Strike (especially if the rage bar is nearing full) will result in a significant increase in threat per second.
In addition, Heroic Strike does not activate the global cooldown and can therefore be used at the same time as another attack. Heroic Strike will dequeue if [Cleave] or [Slam] are activated, as both affect 'the next swing'. Similarly, activating Heroic Strike will dequeue Cleave (or stop a Slam in progress).