Early commentators on the story saw this as merely another tale of terror or horror in which something supernatural was happening. To the modern reader, it is less ambiguous; the beating of the heart occurs within the narrator himself. It is established at the beginning of the story that he is over-sensitive — that he can hear and feel things that others cannot. At the end of the story, if there really were a beating heart up under the floor boards, then the police would have heard it. Clearly, the narrator, who has just finished the gruesome act of dismembering a corpse, cannot cope with the highly emotional challenge needed when the police are searching the house. These two factors cause his heart rate to accelerate to the point that his heartbeat is pounding in his ears so loudly that he cannot stand the psychological pressure any longer. Thus he confesses to his horrible deed. The narrator's "tell-tale" heart causes him to convict himself.
We have here, then, a narrator who believes that he is not mad because he can logically describe events which seem to prove him to be mad. The conciseness of the story and its intensity and economy all contribute to the total impact and the overall unity of effect. In the narrator's belief that he is not mad, but that he actually heard the heart of the old man still beating, Poe has given us one of the most powerful examples of the capacity of the human mind to deceive itself and then to speculate on the nature of its own destruction.
