This is the first appearance of General Wade Eiling who pretty much takes over for General Hardcastle as the military antagonist in the DCAU. This animated version of General Eiling looks different than his comic counterpart because he is designed to resemble his voice actor J.K. Simmons.
During the fight, Vixen, Vibe, and Steel, members of the "Detroit Justice League", are joined together. The Shining Knight and Vigilante, both of the Seven Soldier of Victory, are joined by fellow member S.T.R.I.P.E. (another, The Star-Spangled Kid, was replaced here by Stargirl who also joined them), while two more members, Green Arrow and Crimson Avenger, are paired up.
Included as a bonus cartoon on the bluray release of Justice League: The New Frontier (2008).
The Atom is told, "Save it for the autopsy", when his character had just, in the comics, been deemed responsible by Batman for a killing while Dr. Mid-Nite, shown in scene just before this, gave an autopsy as apparent evidence.
"Dark Heart" gives Warren Ellis as the writer. Ellis is known for high-concept, high-tech, often violent or disturbing comics content -which applies quite well to the episode, which features an interstellar nanotechnology war machine.