In Edgar Allan Poe’s “The Tell-Tale Heart,” the narrator confesses to murdering the old man because of a combination of insanity and guilt.
Although the narrator repeatedly assures us of his sanity, it is quite clear that he is insane. When the police arrive to investigate a scream reported by the neighbors, the narrator convinces them that the scream was his own and the old man is away from home. The police believe this story and do not suspect anything is amiss.
Arrogant and convinced of his own infallibility, the narrator invites the police to sit and chat. As they all talk, the narrator begins to hear a ringing that no one else seems to hear. At first, he is not too alarmed, because the unspecified disease from which he suffers heightens his sense of hearing. The sound grows increasingly louder until it becomes unbearable.
The narrator, not of sound mind, becomes convinced that the sound he hears is the beating of the dead old man’s heart coming from beneath the floorboards where the dismembered body parts are hidden. The narrator becomes paranoid and believes that the police are aware of his guilt and are gaslighting him by pretending they do not hear the sound.
Unable to take the sound and stress anymore, the narrator confesses to killing the old man, rips up the floorboards, and reveals the old man’s body parts.
The narrator confesses because he is insane and irrationally believes that the old man’s heart is still beating even though he is dead. The narrator most likely feels guilty for killing the old man, whom he claims to love. The heartbeat sound is probably a manifestation of his own guilt. His paranoia makes him believe that the police are already aware of his evil deeds, so he confesses to make the sounds he is hearing stop.