Edgar Allan Poe's "The Tell-Tale Heart" uses external and internal conflict to create suspense throughout the short story.
The internal conflict comes from the mind of the narrator of the story. Extremely unreliable, the narrator reveals himself to be mentally unstable early on in the story. He demands the reader take him seriously when he points out, "You fancy me mad. Madmen know nothing. But you should have seen me." The narrator's internal conflict is his struggle with his own mind. He fancies that the odd eye of his old man roommate is evil and must be destroyed. At the end of the story, the narrator's internal conflict consumes him, as he cannot stop hearing the "low, dull, quick sound—much such a sound as a watch makes when enveloped in cotton." His madness overcomes him, and his wild reaction exposes his misdeeds to the police.
The external conflict of the story is the narrator's conflict with the old man. The old man remains seemingly unaware of the narrator's evil machinations and plans to murder him, and the narrator sneaks into his room each night to watch him. Then the narrator pretends nothing is wrong the following day. The external conflict reaches its climax in the moment that the narrator is tormented by the sound of the old man's heart and jumps into his room to smother him to death.
Poe's use of external and internal conflict creates the perfect combination of suspense and danger in "The Tell-Tale Heart."