one's heart is in mouth
(one's) heart is in (one's) mouth
(One) feels extremely nervous, fearful, or anxious. Our hearts were in our mouths as we waited for them to announce the winner.
one's heart is in one's mouth
Fig. one feels strongly emotional (about someone or something). (See also have one's heart in one's mouth.) "Gosh, Mary," said John, "My heart is in my mouth whenever I see you." It was a touching scene. My heart was in my mouth the whole time.