The narrator of "Tell-Tale Heart" defends his sanity – he says he is nervous, but that he can not be called mad. His senses are in fact quickened, and he is more alert and has heard things from both heaven and hell. He admits that his motives for the act to follow are curious, that there was no passion that provoked it. Instead, it was a strange feature of the old man he lives with, that one of his eyes was different from the other and had an evil, vulture-like appearance, which convinced him to kill the old man so that he wouldn’t have to look at it anymore.
The narrator starts by protesting his sanity but such a forceful declaration immediately raises suspicions that he might be misleading us or under an illusion. His inexplicable hatred of the old man’s eye and his fleeting, bizarre mention of heaven and hell create an impression of an eccentric man, who may not be as aware of his own sanity as he claims.
The narrator of "Tell-Tale Heart" thinks we must suspect him of madness again, but we will be dissuaded when we see for ourselves the methodical, patient way that he goes about the murder. For seven nights, he creeps to the old man’s bedroom door, opens the latch, puts an unlit lantern into the room and carefully puts his head in after. Then he opens the shutter of the lantern so that a single ray falls on the eye. Every night, he is annoyed to find the eye closed, because it is its stare that gives him his motivation. The next morning, he always calls to the old man and asks him how he slept.
The narrator seems to think that a person can only be mad if they aren't methodical. But his methodical efforts to kill an old man because he doesn't like the man's eye is crazy! That he needs to actually see the eye to commit the crime makes him seem even crazier. Poe increases and increases the suggestion of madness that he planted at the start of the story.
On the eighth night, the narrator of "Tell-Tale Heart" is particularly gleeful about his sneakiness. He marvels at how the old man knows nothing of his plan. He even laughs a little to himself. But then he thinks he hears the man stirring, but he goes on, gradually putting the lantern inside, knowing that the room is pitch black. But he slips and the lantern chimes and the old man calls out.
The narrator’s chilling laugh, his inability to act until he sees the eye open and his pleasant tone with the old man each morning, combine to make an impression of the narrator as a madman.
For an hour, the narrator of "Tell-Tale Heart" keeps very still and can sense the old man is awake, listening for intruders. The narrator says he knows what this is like. And then the old man lets out a groan, and the narrator recognizes this too, as a sound that comes straight from the soul. The narrator sympathizes but still feels like chuckling. He imagines what the man has been going through since he awoke, trying to explain away the noise and comfort himself but in vain because he feels that Death is in the room.
The strange thing about this rivalry between the narrator and the old man is that it is not really hateful. The narrator seems to have a lot of sympathy for the old man. In fact he knows exactly how scared the old man is, having felt the same mortal terror before. But the narrator’s sympathy is perverted by his strange hatred of the old man's eye.
After a while, without any change to the old man’s obvious alertness, the narrator of "Tell-Tale Heart" opens the shutter a tiny bit and emits a ray upon the man, and sees that the eye is open! The narrator's old fury is stirred at the sight. The narrator reminds us about his quick senses, and begins to hear a dull speedy ticking, which he knows to be the sound of old man’s frightened heart. The narrator keeps still but the heart beats faster and louder. A terrible anxiety seizes the narrator. The heart’s sound increases by the second, until the narrator cannot stand it any longer and rushes into the room with the lantern and pulls the old man onto the floor and kills him by dropping his own bed onto him.
The narrator describes the sight of the eye and sound of the heart as if he is really seeing them, and ascribes the violence of his reactions to his naturally sensitive senses. But Poe engineers the scene so that we suspect that the narrator’s disturbed mind is inventing these terrors and acting self-destructively. The sound of the old man’s heart could well be the sound of his own heart, getting louder the more anxious the narrator becomes.
As the power of the heart and the eye cease, the narrator of "Tell-Tale Heart"’s calm patience return and he says that if there was any doubt that he is sane, his careful disposing of the body will prove it. He works quickly and quietly through the night, dismembering the body and taking up the planks and hiding everything below the room, so that there is no trace whatsoever of the old man.
Each time the narrator has tried to prove his sanity, he has found himself undermining it with confessions of mad behavior. He doesn’t seem to realize that being rational and calm in his murder technique is actually more disturbing than his moments of anxiety.
When the narrator of "Tell-Tale Heart" is finished, it is four o’clock, and he hears the chime of the clock but also a knock at the door. It is the police, who have been alerted to a worrying sound from the address and want to search the property. The narrator smiles, at ease. He explains that the shriek was his own from a bad dream, and leads them around the house and to the old man’s bedroom without nerves, and even places some chairs in the man’s room for the police to rest. He places his own chair directly over the remains.
Poe keeps up the suspense with the coincidence of the police’s call and the chime of the clock. The reminder of the passing of time is nerve-wracking but even more unsettling is the narrator’s apparent calmness. Again, he seems to take his calmness as a sign of his sanity, when in fact it seems to the reader like a signal of his total madness.
The calm manner ofthe narrator of "Tell-Tale Heart" puts the policemen at ease, and they sit and talk, and the narrator talks animatedly at first, but becomes pale and nervous as time drags on. He starts hearing things, a ringing in his head, and he chatters more to try to cover it up but as he talks he realizes that the sound is not coming from his head and is in fact inside the room, it is that familiar ticking, that beating, of the old man’s heart.
The sounds become more frequent and louder, but they cannot possibly be issuing from the remains under the floorboards – they seem instead to be a figment of the narrator’s imagination and we become witness to the true chaos of this man’s mental state.
The narrator of "Tell-Tale Heart" talks faster and louder to try to cover it up and now, panicked, paces the floor. But the policemen, still talking casually, don’t seem to notice. The sound rises above everything, and still the policemen act as if nothing is wrong. The narrator convinces himself that they are fully aware of the crime and are mocking him. He paces the floor, until he loses control entirely and confesses everything, telling the men to tear up the floor boards and that they will find the beating heart.
This is the perfect example of a character whose mind is acting against itself. The narrator’s paranoia leads him to extremely realistic delusions about the suspicions of those around him even though, to the reader, it seems as though they really have no suspicion at all. His psychological instability condemns him before anything else does.