For the patch itself, see August 19, 2008 Patch.
Heavy Update banner TF2
"It's pretty much exactly what we would start a design meeting with. Try coming up with a new unlockable for the Heavy that addresses the goal, while staying within the constraints as much as possible. The extra section includes other details that are useful when trying to compare two viable ideas. Goal: Make the Heavy more viable when he has no Medic to pair with."
Robin Walker

The Heavy Update, officially known as A Heavy Update, was the third major content update for Team Fortress 2.

The focus of the update was the Heavy class. As was customary, three new weapons for the class were revealed, and the slowdown mechanic was introduced. To accompany the Sandvich consumable weapon, Meet the Sandvich was released alongside the update.

A new game mode, Arena, was introduced. It focused on combat between the two teams and brought five new maps to the game. Two other maps, Badwater Basin and Steel, were also included.

The update was released with the August 19, 2008 Patch.