Ventricular fibrillation ( often shortened to VF or V-Fib ) is a cardiac arrhythmia in which there is an uncoordinated contraction of the cardiac muscle of the ventricles in the heart . Ventricular fibrillation ( V-fib or VF ) is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart , making them quiver rather than contract properly .