An exclamation that something is too exciting or overwhelming for one to bear; literally, that it is causing one's heart to beat too fast. In modern usage, it is almost always used sarcastically to imply that something is actually mundane, uninteresting, or unappealing. Usually shortened to "be still my heart." You want me to go shopping with you? Oh, be still, my beating heart! No, thank you. He said the majority of the work I'd be doing for him would entail—be still, my beating heart—copying text from one source to another.