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. You want me to go shopping with you? Oh, be still my heart! No, thank you. He said the majority of the work I'd be doing for him would entail—be still my heart—copying data from one source to another.