fibrillation /fī′brilā″shən/ [L, fibrilla, small fiber, atio, process] , 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 ventricular fibrillation.
