The heart, of course, is vital to human life, its uninterrupted beating a sign that it is functioning and playing its role in circulating blood throughout the body.  Physicians use stethoscopes to listen the beating of the heart.  In one of Edgar Allan Poe’s best known stories, “The Tell-Tale Heart,” that particular organ plays a vital role in revealing the narrator’s incontrovertible madness – his protestations to the contrary.  The narrator is certain of his sanity, and that anybody forced to live with the old man’s “vulture eye” would act in precisely the same manner.  The old man’s eye, which remains open even in his sleep, slowly drives the narrator to a murderous rage.  He is certain that he can hear the old man’s heart beating:

“And now have I not told you that what you mistake for madness is but over-acuteness of the senses?—now, I say, there came to my ears a low, dull, quick sound, such as a watch makes when enveloped in cotton. I knew that sound well too. It was the beating of the old man’s heart. It increased my fury, as the beating of a drum stimulates the soldier into courage.”

Driven with madness to kill the old man and eliminate the source of his anxiety, the narrator finally seizes upon his opportunity and, in his words, entered the old man’s bedroom intent on carrying out the dastardly deed.  The beating of the old man’s heart, however, fills him with a terrible rage:

“And now at the dead hour of the night, amid the dreadful silence of that old house, so strange a noise as this excited me to uncontrollable terror. Yet, for some minutes longer I refrained and stood still. But the beating grew louder, louder! I thought the heart must burst. And now a new anxiety seized me—the sound would be heard by a neighbor! The old man’s hour had come! With a loud yell, I threw open the lantern and leaped into the room.”

The beating of the old man’s heart symbolizes his continued existence.  No surprise there.  That the narrator’s head is filled with the sound of that heart beating ever-louder, however, is maddening.  After he has killed the old man, dismembered his body and buried it under the floorboards, he is visited by three police officers dispatched in response to a report from a neighbor of a loud shriek – the old man’s final protestation.  Certain that the police officers will not locate the hidden corpse under the floorboards, the narrator feels he is safe and has gotten away with murder.   That his head is one again filled with the sound of a beating heart, however, suggests that his psychosis will not allow him the luxury of putting to rest the fate of his victim.  As the beating grows louder in his head, he finally cries out in the presence of the police,

“Villains . . . dissemble no more! I admit the deed!—tear up the planks!—here, here!—it is the beating of his hideous heart!”

The heart symbolizes a guilty conscience.  The old man is most assuredly dead, but the narrator is convinced that his victim’s heart continues to beat and has given him away.  The sound of the beating heart, however, is purely in his head. Poe titled his story "The Tell-Tale Heart" precisely because it is the old man's heart, in the mind of his killer, that tells on him.