tell-tale heart.

Edgar Allan Poe's story is quite a masterpiece. It jumps between reality and fantasy. Some things are unclear, but left for the reader to figure out. One main thing that is never revealed is the relationship of the man and the narrator. They seem to be living in the same house, but it's not stated. I inferred that the narrator was just a worker for the man. Another thing that was left unrevealed was the reason for wanting to kill the man. All that was said was "the eye" bothered the narrator. It bothered him, also scared him, so much that he could not stand looking at it everyday. This reason triggered the death of the man. The last main thing left unsaid was if the heartbeat was real, or just in the narrator's head.
In the story, the narrator tells the reader that he is in fact normal, not "mad". According to the sequence of events, the reader can infer that there is a problem with the narrator. Nobody can hear everything in heaven and hell and still be considered a regular person. He does many crazy things that can lead to the idea that he is a mad man. The first thing is when he tries to plan a way to attack the man in the house. He spends an hour + just trying to open the door without waking the man. After that long time, he finally kills him and shreds him to pieces. Later in the story, the police begin investigating the house because they hear neighbors' complaints. At first, the narrator can reply to the questions asked by the police with ease and no stress. As he begins thinking deeper into the situation, the "heartbeat" grows louder and louder. At last it beats so loudly that he reveals the hiding place of the murdered man without the police pressing him to do so.
In my opinion, the heartbeat was not really there. That is why the police never asked him anything about it. The narrator, being the crazy man that he is, was just hallucinating and imagined the whole thing. If the narrator cut the man to pieces after he captured him, there is no way the man could have still been alive. Maybe the narrator was paranoid, maybe scared? The reader will never know for sure, but he/she can always infer. The story cuts off after the narrator reveals the "hideous heart" and leaves the reader thinking.