Source
The Letters of Emily Dickinson, ed. Thomas H. Johnson and Theodora Ward (Harvard University Press), Letter 262, to Mary Bowles, late spring 1862
Editorial Note
Tracing this line back through Dickinson's correspondence, it appears in her letter to Mary Bowles from around 1862, catalogued as Letter 262 in the Johnson and Ward edition of her letters, where she wrote "The Heart wants what it wants — or else it does not care —." The popular version simply modernizes her capitalization and strips out her characteristic dashes, but the wording is substantively hers. It's worth noting that the shorter fragment "The heart wants what it wants" gained wide currency after Woody Allen used it in a 1992 Time interview, and some catalogues confused matters by hunting for it only among her poems rather than her letters. Once the letter is located, however, the full line matches the attributed quote closely and originates with Dickinson herself. On that basis the attribution is verified.