Be still, my beating heart

‘Beating heart’ has long been used to denote breathless excitement. John Dryden used it with that meaning as early as 1697, in The works of Virgil:

“When from the Goal they start, The Youthful Charioteers with beating Heart, Rush to the Race.”

‘My beating heart’ was a stock expression for 18th century novelists and poets. It is first recorded in Nicholas Rowe’s Tamerlane, a tragedy, 1702:

“My beating Heart Bounds with exulting motion.”

The earliest citation of the full ‘be still, my beating heart’ comes from William Mountfort’s Zelmane, 1705:

“Ha! hold my Brain; be still my beating Heart.”

The expression, and the comic manner in which it is now delivered, were brought to a wide public in Gilbert and Sullivan’s opera HMS Pinafore, 1878:

Ralph:
Aye, even though Jove’s armoury were launched at the head of the audacious mortal whose lips, unhallowed by relationship, dared to breathe that precious word, yet would I breathe it once, and then perchance be silent evermore. Josephine, in one brief breath I will concentrate the hopes, the doubts, the anxious fears of six weary months. Josephine, I am a British sailor, and I love you!

Josephine:
Sir, this audacity!
(Aside.) Oh, my heart, my beating heart!
(Aloud.) This unwarrantable presumption on the part of a common sailor!