Do you feel pity for any of the characters in the story "The Story of an Hour"? Which ones, and why?

Yes, I actually pity both Mr. and Mrs. Mallard because neither of them has the life that they want, and they both want reasonable lives. 

Mr. Mallard wants, I assume, a wife that loves him as much as he loves her.  Mrs. Mallard "had loved him -- sometimes," but her overwhelming feeling upon learning that he has died is joy, a "monstrous joy" but joy nonetheless.  Even she must admit that he "had never looked save with love upon her," and yet, she thinks, "What could love [...] count for in the face of this possession of self-assertion which she suddenly recognized as the strongest impulse of her being!"  Mrs. Mallard doesn't truly love her husband, at least not in the same way that he loves her; her love is uneven, inconstant, and his love is reliable and consistent.  I feel sorry for him that his wife does not reciprocate his feelings.

However, I also pity Mrs. Mallard as well.  She seems to have considered marriage to be the equivalent of a "powerful will bending hers in that blind persistence with which men and women believe they have a right to impose a private will upon a fellow-creature."  Despite her husband's love, she was -- apparently -- unhappy.  She did not feel free, as she repeats the word over and over now as her greatest happiness.  Only now, with her newfound freedom does she feel as though she's "drinking in a very elixir of life."  She used to worry that life would be long, and now she hopes that it will be.  Clearly, marriage was not what Mrs. Mallard wanted.  Perhaps she had no choice; given the time period in which this story seems to be set (the late 1800s), that seems entirely possible.  Marriage was the only respectable choice for a well-off woman.  Mrs. Mallard doesn't want a partner; she wants independence, and she couldn't have it.  She and her husband are unable to have the lives that they want, so I feel for them both.