Heart Troubles - The heart is traditionally a symbol of an individual's emotional core. The first sentence of "The Story of an Hour" informs us that Mrs. Mallard has heart troubles. Her physical heart problems symbolize her emotional heart problems as it relates to marriage.
The Heart (part 2) - The heart of any society is the family and a marriage between a man and a woman is the essential foundation of the family. Mrs. Mallard's heart troubles may represent the peril in which the late 19th century institution of marriage finds itself on account of the inequalities therein.
Mrs. Mallard - Keeping in mind the above examples of an ailing heart, Mrs. Mallard could be said to represent women of her time period who were unable to find happiness in marriage and motherhood, not because it's not found there, but because their freedoms within marriage are restricted.
Spring Time - In her room, Mrs, Mallard "could see in the open square before her house the tops of trees that were all aquiver with the new spring life." Her heart, too, is all aquiver with a new life and a new hope.
Patches of Blue Sky - There were also "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." Light was breaking through what previously had been cover. It's no accident that this light appears in the west, the end of the day. Previously, Mrs. Mallard longed for her life to end, thinking there would be nothing but restrictions. Now that end seems full of hope.
The Chair - Immediately after the news of her husband's death, Mrs. Mallard races upstairs into her room: "there stood, facing the open window, a comfortable, roomy armchair. Into this she sank, pressed down by a physical exhaustion that haunted her body and seemed to reach into her soul." The armchair symbolizes rest from her oppressive life and freedom from societal expectations.