When the lantern's light shines upon the eye, the narrator grows furious. He starts hearing the old man's heartbeat and thinks its so loud that the neighbors might hear it to. He quickly pushes him to the ground and grabs the huge bed.
A few hours after the narrator finishes covering his crime, the police arrive at his house. They had come because a neighbor had heard a shriek and were reported of foul play. The narrator lets them in, and thinks he did not sound suspicious since he was acting extremely confident.
While they were chatting, the narrator starts hearing the old man's heartbeat. He gets paranoid and believes they are mocking him. He became desperate and confessed by showing them the old man's heart.