I was just watching The Wolverine and I was wondering about that little electronic probe wrapped around his heart. Now we all know that that's what caused his healing factor to stumble... But why? Does he get his healing factor exclusively from his heart? Is that canon in all of the comics? And if not then where does he get his healing factor from?
If damage to his heart means his regenerative abilities are stunted, it means one of two things: either the factor originates in his heart, or his blood carries the factor and the heart is necessary to pump it around the body.
The latter makes more sense. After all, even if the factor did originate in his heart, how would it get to all the other organs? It still needs to be in the blood.
So, something which produces chemicals that end up in the blood is probably a factor-production candidate. Which, by the way, isn't the heart. The heart doesn't produce anything, it's just a pump.
Bone marrow produces almost all the blood. However, that isn't too good a candidate, as his own bones got removed. So it has to be an organ that produces something that ends up in the blood, but not necessarily the main components of blood itself.
For instance, the adrenal glands. Top of the kidneys. He still has those, right? They pump adrenaline into your blood, and they often kick in during great stress and/or body damage. I'm putting my money on the adrenal glands.