I read the link.  It says nothing to indicate that this was the first time any one knew he had the symptoms, only that it was news to CNN.  I think it took the MSM close to ten years to "discover" the U.N. oil for food scandal.  The date in which an event is reported is not necessarily the date it occurred.  I wish there were some more dates given; those are always helpful for establishing timelines.  You may be right, that Moore didn't know about Heston's condition before the interview, but unfortunately your source doesn't seems to give us the specific information necessary to even suggest it.  And what is clear, and much more important, is Heston's obvious senility in the film.  If Moore didn't know beforehand, he most certainly must have realised it then.  That was certainly my reaction.  When I first saw the film, I didn't know anything about Moore, and very little about Heston.  Nevertheless, it was excruciatingly clear that Heston suffered from some mental debilitation (I assumed general senility at the time) and lacked the mental capacity to respond.  It was equally clear the Moore aimed to take advantage of this for personal gain. 

 Since you appear to take an objective stance on that portion of the film, try this:  Roughly 1 hour and 48 minutes into the film (this might vary with different copies of the film), moore asks to interview Heston, he is told to show up the next day at 8:30AM.  About 3 minutes and twenty seconds later, a clock clearly shows 6:03.  No reason for this discrepancy is given.  Indeed, if you rewind a little bit further from that position, you will see the clock (showing only the minute hand) pointing about a minute above the 9.  Thus, about 5:46 (possibly an hour or more earlier, but this seems unlikely)  When Heston leaves, the clock can be seen again stating the time to be 6:10.  Moore edited down a 24 minute interview into just a few minutes and the time given that the interview was supposed to have occurred was contradicted within the film.  I suppose that's not much of a big deal, only circumstantial evidence on its own.  What is more important is Hestons OBVIOUS demeanor.  He demonstrates an OBVIOUS lack of the complete mental capacity needed to answer such rapid fire loaded questions, and the filmmaker has edited down the piece a great deal, depriving us of much information that occurred in the interview. 

 Micheal asks a myriad of loaded questions.  For example, "Why do you go to these places (to have gun rallies) after these horrible tragedies?"  NRA meetings are held annually and of a pre-determined time and location.  Moore must've known this, as he is a member.  Heston must've too, but was unable to respond. 

 I had not meant for this conversation to become about a scene within a different Moore film.  If anyone is willing to respond to even one of the blatant deceptions I pointed out (in this film) with some sort of reasonable response, we can continue (begin?) to discuss the issue.