1. Unreliable Narrator: The story is told from the perspective of a mentally unstable murderer. His constant insistence on his sanity, coupled with his increasingly erratic behavior, creates a sense of unease and uncertainty in the reader. We are never fully sure what is real and what is delusion, adding to the tension.
2. Repetition and Sound: Poe uses repetitive phrases and words, especially those related to the old man's "vulture eye." This repetition amplifies the narrator's obsession and intensifies the reader's anxiety. The constant focus on sound, particularly the "low, dull, quick sound" of the beating heart, builds a visceral experience of dread and anticipation.
3. Sensory Details: Poe uses vivid descriptions of the old man's eye, the suffocating darkness of the room, and the sounds of the beating heart to appeal to the reader's senses. This creates a tangible and immersive experience, further heightening the sense of tension.
4. Gradual Escalation of Violence: The story starts with a seemingly harmless observation of the old man's eye, but the narrator's obsession intensifies, leading to the brutal murder. This slow build-up of violence creates a sense of dread and anticipation, culminating in the climactic scene of the police interrogation.
5. Suspenseful Pacing: Poe carefully controls the pace of the narrative. The initial sections are relatively slow, building anticipation for the eventual violence. The murder scene is quick and brutal, followed by a drawn-out and agonizing depiction of the narrator's mental breakdown. This pacing creates a sense of rising and falling tension, keeping the reader on edge.
6. Symbolism: The "vulture eye" can be interpreted as a symbol of the narrator's guilt and paranoia, constantly tormenting him. The beating heart, which he believes he can hear even after the old man is dead, represents the overwhelming weight of his crime. These symbols contribute to the psychological tension of the story.
7. Gothic Atmosphere: The dark, claustrophobic setting and the narrator's descent into madness contribute to a gothic atmosphere that further enhances the tension and dread.
By employing these devices, Poe creates a masterful work of psychological suspense that lingers in the reader's mind long after the story ends.