The story opens with a sentence explaining both that Louise Mallard has heart trouble and that her husband has been killed.
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.
She truly loved her husband and was grief-stricken when she heard the news that Brently had been killed in a railroad disaster. But after she spends some time alone in her room her mood changes. She begins to realize that there is a bright side to her loss. She is free of the bondage of marriage.
She did not stop to ask if it were or were not a monstrous joy that held her. A clear and exalted perception enabled her to dismiss the suggestion as trivial.
"Free! Body and soul free!" she kept whispering.
The irony in the story occurs at the end, when it turns out that her husband had not been killed and in fact was not even involved in the railroad disaster. When he comes bursting through the front door, Louise dies of a heart attack.
When the doctors came they said she had died of heart disease--of joy that kills.
Ironically, it was not joy that killed her but something close to extreme disappointment, even horror at realizing that she was still a captive. No doubt she would not have reacted so strongly to her husband's entry if she hadn't been experiencing so much secret joy in her room at the realization that she was free. It was a combination of sharply conflicting emotions that caused her heart attack.
Naturally, her sister Josephine and the doctors thought that Louise died from the shock of seeing that the man she loved was still alive, but ironically we know, from being privy to her secret thoughts, that she died from the horror of seeing that the man she loved was not dead.
Louise Mallard had enjoyed her freedom for only one hour.
Kate Chopin was a great admirer of Guy de Maupassant. She was fluent in French and translated many of his stories into English. The effect of "The Story of an Hour" is comparable to that of Maupassant's famous story "The Necklace," in which Mathilde Loisel experiences joy in her triumph at the minister's ball, only to be thrown into despair and a lifetime of unhappiness after she loses the diamond necklace.
In Kate Chopin's "The Story of an Hour", it is ironic that all those who witness the death of Louise assume she dies from "a joy that kills". They believe that she has died because the joy of seeing her husband, Brently, alive and well is too much for as she was “afflicted with heart trouble”. Yet, we know that she when believed, for an hour, that her husband was dead “…a little whispered word escaped her slightly parted lips. She said it over and over under hte breath: "free, free, free!" We are also aware that while alone in her room:
Her fancy was running riot along those days ahead of her. Spring days, and summer days, and all sorts of days that would be her own. She breathed a quick prayer that life might be long. It was only yesterday she had thought with a shudder that life might be long.
But as Brently Mallard opened “the door with a latch-key” and walked for the door, Louise’s dream of freedom died and so did she. So, it was not the “joy” that killed her, but her own disappointment of losing her freedom once more. This is a classic example of dramatic irony.