Ventricular fibrillation: An abnormal and irregular heart rhythm in which there are rapid uncoordinated fluttering contractions of the lower chambers (ventricles) of the heart. Ventricular fibrillation disrupts the synchrony between the heartbeat and the pulse beat. Ventricular fibrillation is commonly associated with heart attacks and scarring of the heart muscle from previous heart attacks. Ventricular fibrillation is life threatening.
