The narrator's internal conflict grows more and more tense as he begins to believe that the police officers who have arrived at his door and sit, unknowingly, atop the body of the murdered old man are actually somehow aware of his crime. He thinks he hears the sound of the old man's heart beating beneath the floorboards and that they can hear it, too; however, it is really only his own heart he hears. Nonetheless, the narrator grows more and more anxious, and more upset -- his voice "heighten[s]," and he speaks "more vehemently." He imagines that he rises and speaks in a "high key and with violent gesticulations." He believes, all the while, that the old man's heart beat gets louder and louder and that the officers are only pretending not to hear.
He says, "I foamed -- I raved -- I swore! I swung the chair upon which I had been sitting," and all this time, "the men chatted pleasantly." It seems then, that the narrator isn't actually doing any of these things, but only imagining what it would be like if he did. It is unlikely that the officers would continue to sit and chat pleasantly if the narrator were actually swinging chairs and screaming. All of this tension intensifies the narrator's internal conflict -- to confess or not to confess -- until he finally breaks down and tells the officers what he did.