Contracting in rapid, uncoordinated movements, especially when describing heart muscle fibers that shake instead of pumping effectively.
From Latin 'fibrilla' (small fiber) plus the present participle suffix '-ating'. The term emerged in 19th-century medical literature to describe the abnormal electrical activity observed in heart tissue under microscopes.
Fibrillation happens when your heart's electrical signals go haywire, making the muscle fibers twitch uselessly instead of squeezing together—it's like an orchestra where every musician is playing a different song at a different tempo.
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