Poe is explaining how he is not mad and is telling a story to prove himself. "Nervous --very, very dreadfully nervous . . . How, then, am I mad? Hearken! and observe how healthy --how calmly I can tell you the whole story".
The narrator watches the old man sleeping for seven days but something goes wrong. "I looked in upon him while he slept. Upon the eighth night I was more than usually cautious in opening the door. . . . I had my head in, and was about to open the lantern, when my thumb slipped upon the tin fastening, and the old man sprang up in bed, crying out --'Who's there".
The old man wakes up with a groan, with Poe to be stuck in the same position. "Presently I heard a silent groan of mortal terror."
The narrator hid the body under the floorboards and cleaning up any evidence of the scene. "I then took up three planks from the flooring of the chamber . . . "
Poe confessed about the murder after the heart beat of the old man got louder and louder. "I admit the deed, --tear up the planks, here, here, --It is the beating of his hideous heart".