Poe's use of the first-person narrator who speaks in a very nervous tone and uses twisted logic creates a monologue that reveals his paranoia. This use of first person point of view heightens the tension and dramatic effect of "The Tell-Tale Heart." And, the narrator's monologue itself is a "tell-tale" as it reveals the psychological state of this character.
With debate over the subject of to whom the narrator is relating his tale, some critics feel that the narrative is in the form of a confession, as at a trial or while the narrator is in jail. By the fact that the narrator lays open the details of his murder, he seems to desire to convince his listener/reader of his sanity. Others suggest that the first person point of view is used by Poe to present a parable of sorts to the reader. So says Enotes,
[It is] a parable of self-betrayal by the criminal's conscience--a remarkable record of a guilty mind.