Even the narrator himself appears to be tensioned concerning his account on what happened in the murder room. Whereas his initial narrative is rather slow, he picks up the pace as the storyline progresses, showing that he is discomforted with the overall state of affairs. Although the narrator describes the chain of events leading to the murder and the crime itself as if he would transmit a confession, the fact that he does not keep a steady rhythm makes it difficult for readers to keep up or even to believe him. The fact that the murder story is told with such lucidity virtually makes readers ignore details and concentrate on the more abstract elements of the narrative: the "vulture eye," the heartbeat, and the fact that the narrator constantly stresses how he is perfectly sane.

From the narrator's perspective, everything related to...

Instead of hiding the fact that he is mad, his story only succeeds in highlighting his lunacy. The narrator appears to be well acquainted with the concept of criminals who act out of madness. In contrast to such individuals, he believes that he is mentally healthy precisely because he knew why he killed the old man. Moreover, he believes that he is unlike other criminals as a result of the fact that he did not want the old man dead, given that it was because of the "vulture eye" that he was required to put an end to his friend's life. The narrator's strong connection with his victim in point of fact shows that it would have been impossible for him to have been sane at the time when he committed the murder.
Works cited:

Poe, Edgar Allan. 1843. "The Tell-Tale Heart."