Green’s Dictionary of Slang

heartbreaker n.

[its supposed effect on the opposite sex]

a curled love-lock.

[UK]S. Butler Hudibras Pt I canto 1 line 253: Like Sampson’s Heart-breakers, it grew / In time to make a Nation rue.
[UK]C. Cotton Virgil Travestie (1765) Bk IV 124: A red Heart-breaker next she mow’d off, A Wart that Dido was full proud of .
[UK]J. Dunton Ladies’ Dict. n.p.: A crevecoeur, by some called a heartbreaker, is the curled lock at the nape of the neck, and generally there are two of them [F&H].
[UK]Johnson Dict. Eng. Lang. n.p.: A cant name for a woman’s curls, supposed to break the hearts of all her lovers .
[UK]R. Nares Gloss. (1888) I 412: heart-breaker. A jocular name for that kind of pendent curl which was called a love-lock.
[UK]Farmer Vocabula Amatoria (1966) 4: Accroche-coeurs, m. Small curls on the temples; ‘heart-breakers’; as worn by prostitutes’ bullies.