Be Still My Heart Meaning

(idiomatic) Calm down, this situation is too exciting or overly distressing.

Example: 1868, Charles Reade, Foul Play, ch. 8:
  How strange, how hellish (God forgive me for saying so!) it seems that she should love him. But, does she love him? Can she love him? Could she love him if she knew all? Know him she shall before she marries him. For the present, be still, my heart.
1986, Priscilla Scherer, "Reflections: Daytime Drama," The American Journal of Nursing, vol. 86, no. 1, p. 106:
  Roll tape! Action!
  "I can't feel a pulse!" shouts Ms. Brunette Beauty, RN.
  "Call a code!" commands Blue-Eyed Hunk, MD. . . .
  He's talking to me. Be still my heart.
2004, Michael O'Sullivan, "In Baltimore, Seeing the '(In)visible'," Washington Post, 10 Dec. (retrieved 15 July 2008):
  Calling her installation "information as art," Hesh will have 28 separate documents and artifacts on view, one of which is—be still my heart—a stack of old newspapers.