http://mattzollerseitz.blogspot.com/200 ... heidi.html
It's quite long, so I won't quote the whole thing here, but I especially like his comments on the characters of Kennedy and Heidi, and how they relate to Tony:
Besides mirroring Tony and Chris at various stages of their lives, Kennedy and Heidi also represent the two identities inside so many Sopranos characters -- especially Tony, whose deeply submerged true self (the guy who dotes on his kids, banters with his wife and idealizes young mothers and innocent animals) rarely breaks the surface of his toxic cesspool of a personality. There have always been two Tonys, and in case we hadn't figured that out, Chase gave Tony a cousin named Tony Blundetto, a convicted gangster who'd gone straight, and introduced him in an episode titled "Two Tonys," and then, near the end of the season, had Tony B. impulsively revert to his gangster self and go on a rampage. Kennedy is the voice in Tony's head that says, "Do the right thing." To which Heidi replies, "Fuck that." ...
And he does see the light twice in the episode, literally -- first by looking up at the lamp on the ceiling of his hotel bathroom, then by watching the sunset with Christopher's former stripper girlfriend and erupting with joy at the sight of a solar flare that resembled the helicopter searchlights/operating table lamp from his coma experience. "I get it!" he shouts. "I get it!"
But he doesn't. Any righting of this universe's moral scales will be incidental. Tony's been living an expedient life for too long. If he was going to change, he would have done it. He's been going down this road forever. He's had too many close calls to count. Each time, he hears some version of Heidi and Kennedy in his head, Kennedy saying, "Let's go back," and Heidi saying, "No."
Heidi is driving.