It is a life-threatening heart rhythm that results in a rapid, inadequate heartbeat. It is because the heart doesn't pump appropriate amount of blood during ventricular fibrillation, sustained VF can cause low blood pressure, loss of consciousness and lead to death also. Ventricular fibrillation must be treated as an extreme emergency. Cardiopulmonary resuscitation must be started as soon as possible. It must be followed by defibrillation (an electrical shock delivered to the chest), as soon as the defibrillator is available. Drugs used to treat abnormal heart rhythms may then be given to help maintain the normal heart rhythm. Disordered electrical activity causes the heart's lower chambers. This rapid and irregular electrical activity renders the ventricles unable to contract in a synchronized manner, resulting in immediate loss of cardiac output. Each heartbeat begins with an impulse from the heart's pacemaker (sinus or sinoatrial node). When ventricular fibrillation occurs within a few hours of a heart attack in people who are not in shock and who do not have heart failure, cardioversion restores normal rhythm in 95% of people, and the prognosis is good. People develop irreversible brain damage after about 5 minutes because oxygen no longer reaches the brain. Death soon follows. People who are successfully resuscitated from ventricular fibrillation and survive are at high risk of another episode.