The story is told from the point of view of a man who is trying to convince the reader that he is not insane. He tells the story of an old man who has never wronged him. The old man's cloudy blue eyes bother the narrator so much that every time the old man looks at him, his blood runs cold. So he decides to kill the old man and get rid of those eyes.
He then goes into great detail about how he killed him. He thinks that that the fact that he planned it out so well proves that he is not insane. For a whole week, he would stick his head into the old man's room while he was asleep, never waking him once. On the eighth night, the old man wakes up and yells, "Who's there?" The old man cannot go back to sleep, and finally the narrator shines the light on the old man's evil eye. He hears the beating of the old man's heart. It is so loud that he is sure the neighbors will hear it, so he jumps on the old man and smothers him. The problem is that he can still hear the beating of the old man's heart.
He cuts apart the body and hides it under the floorboards of the house. The neighbors did hear something; they heard the shriek of the old man and called the police. The police arrive to investigate, and the narrator invites them in to check the premises. He says that he was the person who yelled out because he had a bad dream. The old man isn't there because he was out in the country. He takes the police around the house and actually puts chairs over the floorboards that hide the body and invites the police to sit down. Although satisfied with his answers, the police stay and talk. Soon, the narrator starts to hear a ringing in his head. He doesn't want to police to hear it, so he speaks louder and faster. The police don't hear a thing, but he doesn't know that. Finally,he thinks the police are taunting him, and he yells out that he did the deed and they should tear up the planks of the floor. He believes that the sound he was hearing was the beating of the old man's "hideous heart".