In "The Tell Tale Heat," we meet the narrator and the old man, and we see that the setting is in the apartment of the narrators.
The old man
The narrator goes into the old mans bedroom for seven nights. The narrator wants to kill the old man because he thinks his blue hazy eyes can see the inside of him.
The narrator killed he old man. The narrator thinks that once he has killed the old man will not be able to see him anymore.
The narrator "hears" the old man's heart beating, even after he just killed him. The police is talking to the narrator, and he hears the beating of the dead man's heart getting louder and louder.
The narrator feels so much guilt after a few minutes of being in the old man's room that he confesses his crime to the police.
the narrator convinces himself that the old man's heartbeat is audible to everyone and will eventually point him out as his murder, so in a fit of guilt, the murderer breaks down and confesses everything to the police.