Определение и Значение "{one's} [heart] in {one's} mouth"

What is the origin of the idiom "one's heart in one's mouth" and when to use it?

The origin of the idiom "one's heart in one's mouth" can be traced back to ancient Greek and Roman literature. This phrase is often used in storytelling, literature, and everyday conversations to convey a sense of heightened tension or anticipation, such as before a crucial exam, during a thrilling sports match, when confronting a frightening situation, or even during suspenseful moments in movies or books.