Deep feelings or emotions, especially tender feelings like love or compassion; the metaphorical strings of the heart.
Compound word from 'heart' + 'strings,' using the metaphor that emotions are like strings that can be tugged or pulled. Originally from ideas about the heart being attached to nerves.
Medieval anatomy thought the heart had literal strings (nerves and tendons)—so 'tugging heartstrings' started as biology but became poetry. Science gave us the metaphor without knowing it.
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