Ventricular fibrillation is an immediately life-threatening arrhythmia in which the heart's electrical activity and associated contraction becomes disordered and ineffective.
One mechanism believed to be responsible for the rapid, unsynchronized contraction of the ventricles is the continuous reactivation of one or more electrical circuits in the ventricles, which can appear as three-dimensional spiral waves of electrical activity. These waves prevent the ventricles from contracting in a coordinated manner, thereby compromising the heart's ability to pump blood.
Ventricular fibrillation is very serious. Since the heart pumps little or no blood, collapse and sudden cardiac death will follow within minutes unless medical help is provided immediately.