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. The heart is unable to pump blood around the body properly, and ventricular fibrillation can cause tachycardia and hypoxia. Ventricular fibrillation is a medical emergency. If it is allowed to continue for more than a few seconds, the blood will stop circulating, which is what causes the loss of a pulse and respiration, and the person will die.
Ventricular fibrillation is a cause of cardiac arrest and sudden cardiac death. The ventricular muscle twitches randomly when it should contract in unison, and the ventricles cannot pump blood into the arteries and into the systemic circulation.
Ventricular fibrillation can often be reversed by the electric discharge of direct current from a defibrillator. If no defibrillator is available, a precordial thump can be delivered at the onset of VF to regain cardiac function, but they are not always effective. Antiarrhythmic agents such as amiodarone or lidocaine can help, but, unlike atrial fibrillation, ventricular fibrillation rarely reverses spontaneously in large adult mammals. Although a defibrillator is designed to correct the problem, it is not always successful.
In patients at high risk of ventricular fibrillation the use of an implantable cardioverter-defibrillator has been shown to help.