Answer:
The beating heart in "The Tell-Tale Heart" symbolizes the murderer's conscience and/or his guilt.
Explanation: It seems as though this man knows that he has committed a horrible crime and the guilt is literally destroying him, eating him up inside like a living creature fighting its way out. Though a manifestation of his mind,the beating heart is real enough to him to drive him to the verge of insanity and to an admission to the crime.
