Whenever it fell upon me, my blood ran cold; and so by degrees — very gradually — I made up my mind to take the life of the old man, and thus rid myself of the eye forever.

The narrator here provides as much of an explanation as we get as to why he decides to murder the old man. The old man’s eye makes him feel so uncomfortable he becomes convinced it means him harm. The only solution he can imagine is to kill the old man. This moment reveals the irrationality of his thought process. He projects malice onto the eye even though he is the only one seeking to do harm. He further decides being free of the eye is so important that he considers the old man acceptable collateral damage.

I saw it with perfect distinctness — all a dull blue, with a hideous veil over it that chilled the very marrow in my bones; but I could see nothing else of the old man’s face or person: for I had directed the ray as if by instinct, precisely upon the damned spot.

The narrator describes how on the eighth night, when he illuminates the old man’s eye, he catches it open. Through this trick of the light, the narrator has managed to visually separate the old man’s eye from his person, the part of the old man the narrator hates from the part that he loves. During the previous nights, when he illuminates the old man’s eye, he has found it closed, and therefore could not focus on his hatred of the eye and commit the murder.

Yet the sound increased — and what could I do? It was a low, dull, quick sound — much such a sound as a watch makes when enveloped in cotton.

This quotation appears as the narrator sits chatting pleasantly with the police and first begins to hear the heartbeat. The description of a sound, that of a watch covered in cotton, echoes how he earlier describes the old man’s terrified heartbeat when the narrator accidentally wakes him. The comparison of the heartbeat to a watch makes the sound seem like a countdown. The real sound counted down to the old man’s death. When the narrator hears the sound again, be it real or imagined, it counts down to his confession.

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

In the famous final line of the story, the narrator confesses to the old man’s murder. Even though the police appear to have suspected nothing up to this moment, the narrator brings about his own downfall by confessing. It’s unclear whether the narrator has hallucinated the sound of the heartbeat altogether or mistakes the sound of his own racing heart for that of the old man’s, but either way, it’s clear that he can no longer sit with the knowledge of his guilt. Although he blames the police for his torment, in reality he has tormented himself.