Heart of Darkness

I had seen the movie "Apocolypse Now" many years ago. I am looking forward to watching the movie on Saturday. I am really interested in seeing how Mr. Crandall states that this movie is like the story "Heart of Darkness". I think discussing the movie with the class is going to open a whole new way of interpeting the movie. Has anyone who remembers the movie, Apocolypse Now, see the similarity of the story "Heart of Darkness"?