The story's very structure is built on ironic juxtapositions. The elements that will later destroy Mrs. Mallard can all be found in the very first paragraph:
Knowing that Mrs. Mallard was afflicted with a heart trouble, great care was taken to break to her as gently as possible the news of her husband's death. (1)
Her health, the corresponding condition of delicacy, and the danger of unexpected news are all highlighted. In a twisted way, Mrs. Mallard becomes prepared for her husband's death, but not his life. You might notice that this sentence is written in the passive voice: "great care was taken" to tell Mrs. Mallard the news. The people who take care of Mrs. Mallard this way, though, aren't mentioned until the next paragraph.
Plus, Chopin's whole writing style in this story is kind of a tease. She forces the reader to fill in the blanks. Consider, for example, the way she describes the end of the story. Mrs. Mallard is coming down the stairs when her husband, who is supposed to be dead, walks in; the couple's friend Richards tries to move between them to keep her from sustaining a potentially deadly shock. The narrator simply says, "But Richards was too late" (22). What Richards is "too late" to do, precisely, is left to the reader's imagination.
The next paragraph simply reads, "When the doctors came they said she had died of heart disease – of joy that kills" (23). Between "too late" and "When the doctors came," Mrs. Mallard has died. Yet the precise details of her death go unmentioned; the feelings she might have had go undescribed. This is ironic considering how detailed the narrator has been in sharing with readers the feelings Mrs. Mallard had been experiencing alone in her room. Now, in the most shocking moment of her life, nobody knows what Mrs. Mallard feels.