The worst aspect of the death scene in Edgar Allan Poe's "The Tell-Tale Heart" comes from the narrator's own perception of his murderous deed.  His point of view as he murders the helpless old man is not only deranged, but also disgusting.  The beginning of the scene feels extremely predatorial to the reader as the narrator watches and listens to the heartbeat of the old man.  His heartbeat, which establishes itself as a major motif of the story in this scene, is a vocal reminder to the narrator of the old man's continued presence in the house.  The narrator hears the "hellish tattoo" which taunts the narrator, stirring him into a murderous frenzy. 

After the narrator attacks his elderly roommate, pulling the mattress over his prone form, he "smiled gaily;" his pleasure at the simplicity of this act of murder is absolutely disturbing and offensive to the readers.  Poe continues to increase the morbidity of the scene.  If the narrator's satisfied response was not enough, he also includes the details of the continued murmur of the old man's heart, thus intensifying the horror. 

Poe uses his unreliable narrator and the rhythm of the old man's heart to construct a death scene both horrible and chilling.