At the end of "The Story of an Hour," the doctors think Mrs. Mallard died of "joy that kills" because they believe she was so overwhelmed by the sudden joy of seeing her husband alive—whom she thought was dead—that her weak heart could not handle it. The text supports this with the detail that Mrs. Mallard had a known heart condition, which made emotional shocks particularly dangerous for her. The doctors mistakenly interpret her death as a result of overwhelming happiness or joy upon her husband's return. However, this diagnosis is deeply ironic and inaccurate. The evidence from the story reveals that Mrs. Mallard's true feelings were quite the opposite. When she learns of her husband's death, she feels a complex mixture of grief and an unexpected sense of freedom and relief at the prospect of living her life for herself. She even envisions a future of independence and joy without her husband's control. When her husband unexpectedly returns alive, this hope and freedom are instantly crushed. The shock and despair of losing her newly imagined freedom cause her fatal heart attack—not joy. Key evidence from the text includes Mrs. Mallard retreating alone to her room where she experiences a "monstrous joy" in the revelation of freedom, crying tears "of grief" that are more complex than simple sorrow, and the final moment where she dies upon seeing her husband alive. The story's irony lies in the contrast between the doctors' superficial diagnosis and the profound emotional and psychological reality experienced by Mrs. Mallard, which only the reader understands.

In conclusion, while the doctors assert Mrs. Mallard died from the joy of seeing her husband alive, the text clearly supports that it was the loss of her brief glimpse of freedom and the ensuing shock that truly caused her death. The doctors' diagnosis reflects dramatic irony and societal misunderstanding of Mrs. Mallard's inner life.