The open window signifies the new life and the fresh start that Mrs. Mallard believes she will have now that her husband is dead. We often open windows in our home to let in fresh air and let out stale air, correct? Mrs. Mallard is doing the same thing, symbolically, of course. She is releasing the old way of life she had and letting in the new life she hopes to have; however, she will never get the chance to do so because she dies upon seeing that her husband is actually not dead.
For Louise Mallard, the open window represents the freedom she feels when she learns that her husband has died. In her epiphany she realizes she is now "free, body and soul" to live her own life. When she looks out this open window, she sees spring (symbolic of her new beginning), an open square (also represents freedom), and a blue sky (symbolic of hope).
The passage concerning the open window is rich in symbolism in this early feminist story published in 1894.
She could see in the open square before her house the tops of trees that were all aquiver with the new spring life. The delicious breath of rain was in the air. In the street below a peddler was crying his wares. The notes of a distant song which someone was singing reached her faintly, and countless sparrows were twittering in the eaves. There were patches of blue sky showing here and there through the clouds that had met and piled one above the other in the west facing her window.
Louise is able to look to the West through her open window. In the late 19th century, the American West was still seen as a place of immense opportunity--suggestive of the opportunities Louise will have outside her marriage. There are signs of spring everywhere: newly green leaves and the promise of rain to nourish them, active birds, blue skies--all harbingers of the new life Louise will be able to enjoy as a single woman. The peddler's wares represent, perhaps, new things that Louise will be able to bring into her life that may not have been possible in the oppression of her marriage. A distant song--close enough to be heard--suggests more beauty that is now coming closer to Louise's grasp.