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fibrillation (fy-bril-ay-shŏn) n. chaotic electrical and mechanical activity of a heart chamber, which results in loss of synchronous contraction. The affected part of the heart then ceases to pump blood. atrial f. (AF) a common type of arrhythmia that results in a rapid and irregular pulse rate. The main causes are atherosclerosis, chronic rheumatic heart disease, and hypertensive heart disease. ventricular f. (VF) fibrillation that causes the ventricles to stop beating (see cardiac arrest). It is most commonly the result of myocardial infarction.

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fibrillation Non-rhythmic and mechanically ineffective contractile activity in the heart muscle, associated with disordered electrical activity. Atrial fibrillation is not uncommon, and not in itself a serious threat: the heart can function without effective contraction of the atria, because the main pumps (ventricles) continue to beat effectively (though not regularly). But ventricular fibrillation stops the pump and is fatal, unless it can be promptly reversed.

Stuart Judge

See defibrillator; heart; pacemaker.