Overwhelmingly sad, especially from romantic disappointment or loss.
Compound of 'broken' (from Old English 'brocen') and 'hearted' (from Old English 'heorte'). The phrase became fixed in the 16th century as a way to describe deep emotional pain using the metaphor of the heart as the seat of love and emotion.
We describe emotional pain through broken machinery ('broken heart,' 'shattered,' 'falling apart') because medieval people thought the heart was the literal source of emotion—but neuroscience shows the brain controls feelings, yet we never updated our metaphors, so we're still speaking medieval cardiology.
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