In Edgar Allan Poe's "The Tell-Tale Heart", the irony is mostly found in the seemingly bipolar emotions of the narrator; a disturbed man who combines love with hate, as well as punishment with mercy, to act upon the old man who lives with him.
The irony begins from the very beginning, when the narrator explains his rationale behind killing the old man:
Object there was none. Passion there was none. I loved the old man. He had never wronged me. He had never given me insult. For his gold I had no desire. I think it was his eye! yes, it was this! He had the eye of a vulture --a pale blue eye, with a film over it. 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 odd and contradictory ramble shows the aberration of it all: The narrator feels an underlying type of sick and psychotic love for the man. He even admits that the man has been nothing but good him.
In a separate irony, he admits that his carefully-planned murder, though well-orchestrated, had "no object, nor passion." One must wonder: Then, why even do it? The answer goes back to the beginning. The man is insane, and this is what causes his ironic shifts of thought-and his rationale for murder.