Answer :
Answer: What kills Mrs. Mallard is actually disappointment upon seeing her husband alive.
Explanation:
The irony in this short story is that contrary to the doctors claiming that Louise died of a heart attack due to the happiness of discovering her husband hadn´t died, she died because she was sad about it.
When Mrs. Mallard was told that her husband had died, she went to her room where she secretly thank her luck for having the chance to have a better life without the opression of marriage. When she discovers that her huband is alive, she dies of a heart attack, which the doctor ironicaly believe is caused by a shocking happines.