What is be still my heart?

"Be still my heart" is an idiomatic expression used to express shock or surprise. It is often used when someone sees, hears or experiences something that takes their breath away, or when they are particularly impressed or moved by a person, event, or thing. The phrase is often used romantically or emotionally, and is commonly seen in songs, literature, and poetry. It can also be used in a humorous way, to indicate that the speaker is pretending to be more impressed than they really are. Overall, "be still my heart" can be interpreted as an expression of intense emotion and passion.