In Poe's short story "The Tell-Tale Heart," the narrator murders an elderly man and disposes of his body under his floor. When three policemen knock at his door, he lets them in, confident that they will not be able to connect him to the crime. However, he soon begins to hear a sound that gets louder and louder. He thinks the policemen must hear it, too. Ultimately he breaks down and confesses, and we learn he thinks the sound is the beating of the man's "hideous heart."
The heart is a symbol in this story, and it works on at least four levels. We associate a heartbeat with life, so the beating is a reminder to the narrator that he has stolen the life of the elderly man. A heart is also the symbolic seat of the emotions. The narrator has been "heartless" in murdering a man who has done him no wrong and toward whom he actually feels no personal animosity. It is only the man's eye that the narrator despises. So there is irony in having a symbol of emotion be the thing that gives the heartless murderer away. Third, the heart is also the symbol of the conscience. We often say, "I knew in my heart it was wrong." The narrator has no conscience; after he murders the man, he does not feel guilty and is even happy to let the police in; he even "placed my own seat upon the very spot beneath which reposed the corpse of the victim." Since the narrator has no active, beating conscience in his own chest, the heart of the murdered man rises up to protest what the murderer has done. As much as the narrator has tried to bury his emotions and his conscience, he cannot keep them quiet, and they eventually accuse him of his dastardly deed. Finally, the heart is the symbolic location of good or evil inside a person. We say a person has "a good heart" or "a wicked heart." Ironically, while the narrator labels the murdered man's heart as "hideous," we know it is the narrator who has a "hideous heart."
Poe uses the heart as a symbol of life, emotion, conscience, and evil in this story, often with a twist of irony.