The denouement of The Story of an Hour by Kate Chopin occurs when Mrs. Mallard reacts to the sight of her husband after she had been told that he was dead from an accident.

According to the story,

Someone was opening the front door with a latchkey. It was Brently Mallard who entered, a little travel-stained, composedly carrying his grip-sack and umbrella. He had been far from the scene of the accident, and did not even know there had been one. He stood amazed at Josephine's piercing cry; at Richards' quick motion to screen him from the view of his wife.  

When the doctors came they said she had died of heart disease--of the joy that kills. 

This is a significant matter considering that, earlier on, Mrs. Mallard was literally breathing for the first time “the elixir of life” that came with the news. We learn that Mrs. Mallard felt that she was finally free from what we can assume was a tedious and unwanted marriage. The joy that befell her was greater than anything, and made her already-weakened heart palpitate with the emotion one feels when a burden is lifted.

One must not forget that the position of women in society at the time this story was published was not the most optimal. Women were merely a social fixture whose only purpose was to breed, nurture, and care for a home. Marriage was basically the only choice for women to be in society. However, we also know that many marriages were arranged and many women were emotionally and sexually dissatisfied.

Hence, when Mrs. Mallard’s shock to see her husband was strong enough to kill her, one can imagine that Mr. Mallard’s presence in her life was unbearable. Seeing him again would mean to give up that sensation of freedom that she so cherished. To add to the irony, her cause of death was said to be from a “joy that kills”. The reader knows that her death came actually from the shocking disappointment of seeing her husband again.  Therefore the way this affects the overall theme of the story is that Mrs. Mallard’s desperate for freedom became a silent cry for help that maybe even manifested itself in her weakened heart.  When she saw that she had to give up the sensation of liberation she felt for the first time in years, her weakened heart gave up, and she became free in eternity.

The denouement or resolution of Kate Chopin's "The Story of an Hour" occurs at the very end of the story with surprising force.

Mrs. Louise Mallard, who has heart trouble, has been told that she is free from the restrictions of her marriage by the untimely death of her husband. Without having realized it before, she soon understands that her will has not been her own, but has been controlled by her husband, who had generally been kind and whom she had sometimes loved.

However, now Mrs. Mallard's new sense of freedom gives her a renewed interest in her life. Whereas the day before she had worried that life would be long, now she prays that life will be long because she realizes that she has been set "free." "Body and soul, free."

When, at the story's conclusion, Louise Mallard finally leaves her room and goes down the stairs with her sister-in-law, a key in the door announces the arrival of...her allegedly dead husband, Brently. He was not killed in a railway accident as reported. In that moment, rather than being overjoyed at his "resurrection," Louise loses the promise of freedom widowhood would have brought her.

The denouement is the doctors' diagnosis:

When the doctors came they said she had died of heart disease—of joy that kills.

The irony is, of course, that she did not die from the joy of seeing her husband  alive, as they believe, but of disappointment at the loss of her dreams for a life all her own. The story reflects the importance of the title—that within an hour Louise's life changes enormously: she gains a life and loses it. The story also perpetuates the sense of society (then) that a woman's happiness depended upon having a husband. Independence was not something women needed:  why would they with a husband to make the important decisions?

Overall, the theme throughout the story is Louise's discovery of the value of independence for a woman. The denouement reflects society's inability to understand this concept: the doctor's blame her death not on disappointment, but on ill-health, something only the reader would be able to pick up on.