have (one's) heart in (one's) mouth
To feel very nervous or anxious. I had my heart in my mouth as I waited for the ambulance to arrive.
have one's heart in one's mouth
Fig. to feel strongly emotional about someone or something. (See also one's heart is in one's mouth.) I had my heart in my mouth when I heard the national anthem.
have (one's) heart in (one's) mouth
To be extremely frightened or anxious.