Uncoordinated contraction of the muscle fibres of the heart's ventricles (see arrhythmia). Causes include heart attack, electric shock, anoxia, abnormally high potassium or low calcium in the blood, and digitalis or epinephrine poisoning (see drug poisoning). Death soon follows if circulation is not restored with electric shocks (defibrillation) or drugs supplemented by chest compressions (as in cardiopulmonary resuscitation). Seealso atrial fibrillation.

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