Involuntary recurrent contraction of a single muscle fiber or of an
isolated bundle of nerve fibers. Fibrillation of a chamber of the heart
results in inefficient random contraction of that chamber and disruption of
the normal sinus rhythm of the heart. Fibrillation is usually described by
the part that is contracting abnormally, such as atrial fibrillation or
The large arteries and veins arising from the heart and pericardium.