heart-in-mouth
/ˌhɑːtɪnˈmaʊθ/adjective
That causes great apprehension or alarm; anxious; thrilling. Compare to have one's heart in one's mouth.
adverb
Usually without hyphens. Anxiously; apprehensively; with trepidation.
Origin
Early 19th century (in an earlier sense). From heart + in + mouth.