1
general::
Phrase(s): lose heart
Fig. to lose one’s courage or confidence. • Now, don’t lose heart. Keep trying. • What a disappointment! It’s enough to make one lose heart.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Become discouraged, as in The rescuers worked hard for the first few hours, but then they lost heart. This term uses heart in the sense of "courage" or "spirit." [Mid-1800s] Also see LOSE ONE'S HEART TO.
American Heritage Idioms