What does fibrillation mean?
Fibrillation refers to a rapid, chaotic, and uncoordinated contraction of muscle fibres, most importantly in the heart. Instead of contracting as one unit to pump blood, the affected chambers quiver ineffectively, producing no true pulse. The term covers two major conditions: atrial fibrillation, the most common sustained cardiac arrhythmia, in which the heart's upper chambers tremble irregularly and raise the risk of stroke; and ventricular fibrillation, in which the lower chambers lose all effective rhythm — a medical emergency that causes cardiac arrest within seconds. Derived from Latin 'fibra' (fibre) via 'fibrilla' (small fibre), the word literally describes many tiny fibres each firing on their own. Fibrillation belongs chiefly to medical language, appearing constantly in cardiology reports and health journalism, and it is closely associated with defibrillation, the electric shock that restores normal rhythm. Its vivid literal image — a heart reduced to trembling threads — makes it one of medicine's more memorable coinages.
nounRapid, irregular, and unsynchronized contraction of muscle fibres, especially of the heart, in which the affected atria or ventricles quiver instead of beating effectively.
- A cardiac arrhythmia in which the atria (atrial fibrillation) or ventricles (ventricular fibrillation) contract rapidly and irregularly instead of in coordinated beats.
- By extension, any similar rapid irregular twitching of muscle fibres, such as fibrillation of skeletal muscle observed in certain neuromuscular disorders.
"The paramedics used a defibrillator to shock the patient's heart out of fibrillation."
"Atrial fibrillation affects millions of older adults and raises the risk of stroke if left untreated."
"The electromyogram detected spontaneous fibrillation in the denervated muscle."
The plural is rare; it typically occurs when referring to repeated episodes or to fibrillations observed in multiple muscles during electrodiagnostic testing. Most usage keeps the word singular.
"The EMG showed frequent fibrillations in three of the muscles examined."
During fibrillation the heart doesn't beat at all — it simply quivers like a bag of worms, which is why an electrical shock is needed to reset it.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of fibrillation
Fibrillation derives from New Latin 'fibrilla', a diminutive of Latin 'fibra', meaning fibre or filament, and entered English medical usage in the nineteenth century as physicians began describing the fine, worm-like quivering of heart muscle. It shares its root with English cognates such as 'fibre', 'fibrous', 'fibril', and 'fibrin'. The related verb 'fibrillate' and the life-saving term 'defibrillation' were formed directly from the same stem.
Related word forms
How fibrillation is actually used
Fibrillation is a technical medical term, common in clinical and cardiological contexts rather than everyday speech. It almost always appears with a specifier — most often 'atrial' or 'ventricular' — since the two forms differ greatly in urgency: ventricular fibrillation is immediately life-threatening, while atrial fibrillation is chronic but serious. The word carries a strongly negative, alarming connotation.
Easily confused with fibrillation
Flutter is a rapid but organized, regular heart rhythm, whereas fibrillation is chaotic and disorganized.
Defibrillation is the electrical treatment used to stop fibrillation, not the condition itself.