The beating heart can also represent the growing excitement within us, the audience, as the crime is about to be discovered. We find ourselves horrified with the deed that the narrator has committed, but equally fascinated as to whether or not he will escape detection. The pace of sentence structure speeds up and becomes as disjointed as the narrator's thought processes. The beating heart can therefore also be ours as we become involved in the narrative.
The narrator is of course unreliable; if he is telling the truth, he is certainly criminally insane. He is obsessed with the old man's eye and the sound of the beating heart. I think that the beating heart represents the cadence of the narrator's own conscience. His guilt over the murder, whether it was real or only in his own mind, won't be silenced.
The narrator of this story has just killed a man and stuffed him under the floorboards, and he has spent a good amount of time, as he tells the story, trying to justify his actions to a seemingly unsympathetic audience. Right from the beginning he proclaims he is "not mad", and that he had good reason for what he did; this indicates that he is defensive, and feeling guilty for his crime. As he recounts the tale, the beating heart starts only after the crime has been committed, and gets more and more intense the more he tries to confidently deny his crime. So, the beating heart symbolizes the narrator's conscience, or his sense of guilt and wrongdoing. After all, he HAD killed a guy. Outwardly, he seems cocky and unregretful. He asks, "what had I to fear" from the cops? And it was in "the enthusiasm of my confidence" that he seats them right on top of the body. So, to look at him, or hear him describe it, he had no guilt. However, Poe decided to symbolize this man's subconscious guilt through the heartbeat. Since the narrator himself refuses to admit any wrongdoing for killing the man, Poe had to show that he did feel bad at some level, and chose to do that through the heart. It symbolizes how what he did cannot be hidden from himself, or from the old man. He feels guilty; each beat of the heart reminds him of his crime, and it is that, his guilt, that leads him to confess.
The beating heart is symbolic of our narrator's intense feelings of guilt over the macabre act he has committed. When investigators show up at his door, his own beating heart begins to plague him, and our narrator hears it as the victim's beating heart beneath his floorboards.
In a schizophrenic state of terror, the narrator rips up his floorboards to reveal the horrific act he has committed; a direct result of his own heartbeat mimicking that of his deceased victim. In this sense, the beating heart can represent truth, or the need for it, in all our lives.
I agree with ghalam--sometimes we do literature a disservice by looking for deep symbolic meaning behind every door and under every rock (floor board if you preferJ). The beating of the heart has always seemed to be simply his own. Like in times of great stress when we can almost feel the ebb and flow of blood or hear the beating of our own heart in our chest.
I always related the beating of the heart to the beating of the narrator's heart. As mentioned several times above, the narrator is having extreme feelings of rage, guilt, and fear so it is likely that his own heart is racing at this point in the story. Because he is dillusional, he cannot divorce the reaction of his own person from what he suspects is that of the old man.
Kudos to Kiwi for noticing how Poe varies the sentence structure in his story "The Tell Tale Heart" in order to increase the pace of the story. Clearly this story is meant to have tension for both the character and the reader. Early in the story, the narrator blithely claims that he is not insane, and yet all of his actions indicate the exact opposite is true. That being said, after he kills the old man, he can't admit it was wrong (or he shouldn't have done it). So Poe has to create an environment in which we as readers recognize the craziness of the narrator without forcing the narrator to recognize it. This is perhaps why the narrator hears the nonexistent heartbeat. It emphasizes the insanity of the narrator more effectively than any other strategy.
That's an excellent question, and one which has plagued readers of Poe's story since its publication. Frankly, there are a number of ways we can understanding what the beating heart symbolizes in the story. Some critics have argued that the heart symbolizes the narrator's guilt or his own fear. Other critics view the symbol of the beating heart to be symbolic of the narrator's own insanity. Remember, because the story is narrated through only the perspective of the narrator himself (who is unreliable and, as we must keep in mind, is probably not meant to be Poe himself), then the beating heart itself might only exist within the imagination of the narrator and might not be "real."
The beating heart symbolizes the narrator's guilty conscience. At the end of the story the narrator says, "Here...here...it is the beating of his hideous heart." This shows that, although the narrator was vexed by the old man's eye, it is ultimately the old man's heart that needs to stop beating in order for the eye to "trouble him no more."
The narrator is hearing his own heartbeat, due to his guilty conscience. Haven't we all heard our own heartbeat when we get excited or feel afraid? He attributes the sound he is hearing to the corpse under the floorboards because he knows he has done something wrong. He also senses that he will not get away with it for long, especially since the corpse will start to smell after a while. I am not so sure that the narrator is insane. His actions seem too deliberate, and if he was insane, he wouldn't have any guilt.
I think we shouldn't make a symbol of everything in literature. Rather than being a symbol of something, the heartbeat he hears can be some illusional sound which he hears due to his increasing insanity.
The "beating heart" in "The Tell - Tale Heart" symbolizes the narrator's own guilt or guiltiness. It would be from the narrator's own heart because one, the narrator just killed the old man, which would make him feel guilty. Two, the old man is dead so it would obviously won't come from the dead, old man. The narrator doesn't realize himself that he feels guilty, but it bothered him so much that he had to confess to the police.