How does repetition and the slowing down of action create suspense in "The Tell-Tale Heart"?
Repetition is what lets the reader understand the level of anxiety and obsession that the narrator feels. By pointing out the same thing, by repeating himself so much, and by consistently making the same point one realizes that this person is out of his own control, and that an outside force is what is driving him.
Added to this, the slowing of the action gives the reader a sense of emptiness that invites the idea that something big is about to happen, like the calmness prior to the storm. The rythm winding down, the narrative slowing down, and the energy of the story slowing down makes us curious, and immediately after something unexpected will happen. It is like a scary movie: Suspense, then action.