There are two dominant elements in Poe's story. One is insanity. The other is the narrator-protagonist's motivation to commit a perfect crime of murder. It is because he is insane that his perfect crime plan fails. He imagines he can hear the beating heart of his victim, even though he has cut the body into pieces. Throughout the narrative the protagonist is trying to convince the reader he is sane, and all the while he is doing just the opposite, displaying insane delusions. At first he is motivated to commit the murder because of the old man's eye, and then he confesses to the murder because of his fixation on a heartbeat which is probably his own heart he can hear beating because of his extreme nervousness. The reader identifies with the madman because of the first-person narration, and hence the reader is forced to share his fear and his delusions.