The second expansion for Fallout: New Vegas, named Honest Hearts, was released on May 17, 2011 on Xbox Live and Steam and June 2, 2011 on the PSN due to the April—May PSN outage. In Honest Hearts, the Courier is part of an expedition to Utah's Zion National Park, when they are attacked by tribal raiders. While trying to return to the Mojave, the player becomes involved in conflicts between the tribes and between a "New Canaanite" missionary and individual known as the "Burned Man", Caesar's former Legate, who, after losing the first battle of Hoover Dam, was covered in pitch, set on fire, and thrown into the Grand Canyon.
The pack adds new achievements/trophies, perks, terrain, enemies and decisions for the player, as well as raising the level cap by 5. Chris Avellone has confirmed that the locations in Honest Hearts and all DLC's following it will still be accessible even after completing that DLC (in contrast to Dead Money, which is closed off after completing it). The "companion bug", which prevented players from entering Zion, was fixed in the 1.7 update. Players are now able to use an in-game console to dismiss all companions.
After the First Battle of Hoover Dam, Caesar sent Ulysses to Great Salt Lake to rally the White Legs to destroy New Canaan. With his help, the White Legs found a large supply of weapons artillery. The White Legs then destroyed New Canaan, sending Joshua Graham, the Burned Man, and the New Canaanites to the Zion Canyon, where the Dead Horses stand with them against Caesar. The Courier then arrives in the Zion Canyon and meets the Burned Man Joshua Graham who is surprised that it is a different Courier than Ulysses that came to him, as he had figured Ulysses would come to murder him. This sparks the beginning of Honest Hearts.
Source: Wikipedia, "Fallout: New Vegas", available under the CC-BY-SA License.