What does the heart beating represent in "The Tell-Tale Heart" by Edgar Allen Poe?

Edgar Allen Poe is the master of the gothic tale, and the
narrator's hearing the heart beat of the old man he killed, dismembered, and buried
under the floor boards, is a classic example of the supernatural element that is so
common in his stories.  In this case, the heart beat comes to signify the guilty
conscience of the narrator.  He tells us that he is not crazy when he kills the man, but
that he was driven to kill him by some urge and that the old man's eyes finally drove
him over the edge.  Once he hides the body, he probably would have gotten away with the
crime, but when the police come on an unrelated matter, he is so consumed by his guilt
that he thinks he hears the heart beating and as it gets louder and louder, just as his
guilt grows with every minute that passes, he eventually blurts out the truth -- he
can't take the sound of the heart beating and must alleviate himself of the oppressive
secret -- and his guilt.