"And then, when my head was well in the room, I undid the latern cautiously-oh,so cautiously- cautiously(for the hinges creaked)-I undid it just so much that a single thin ray fell upon the vulture eye."
"It grew quicker and quicker, and louder and louder every instant"
In this picture, the narrator is mentioning how he murdered the old man. He mentioned that he was kind to the old man the whole entire week before he murdered him. In this picture, the narrator is also telling us about how he would shine a small ray from on the lantern to see if the eye was open. The narrator did this every day for 7 days.
"It was wide wide wide open-and I grew furious as I gazed upon it."
"I then took up three planks from the flooring of the chamber, and deposited all between the scantlings."
In this picture, the narrator checks to see if the old man's eye is open. Then to the narrator's surprise, the lantern shown out light and the old man arose and frightenedly asked who was there.
In this picture, we see the old man frightened and the narrator hears the old man's heartbeat and it won't go away. It is driving the narrator mad until he can't take it any longer.
"I admit the deed!-tear up the planks!-here, here!-it is the beating of the hideous heart!"
The lantern finally falls onto the old man's eye. That was the last straw for the narrator. He killed the old man. The old man was not the narrator's problem it was the eye.
The narrator dismembers the body of the old man and puts the limbs underneath the planks of the floor. He cut the man up in the bathtub so there was no blood to worry about. He knew no one would ever know. But then something struck the mad narrator he could still hear the old man's heart beating yet there was no pulse.
The police arrived and spoke to the narrator about a weird scream heard from the neighbors. The narrator was confident they wouldn't find anything. But the heart continued to beat. It drove him mad. He confessed to the murder. All along it was his own nervous and terrified heartbeat.