Ventricular fibrillation (VF) is a life-threatening type of abnormal heart rhythm (arrhythmia) in which the heart “quivers” rather than beats, sometimes at a rate of 350 beats per minute or more. As a result, adequate blood flow throughout the heart and the rest of the body is drastically reduced. VF is a cardiac emergency that requires a rapid response. Studies have shown that a person cannot survive more than about four minutes in ventricular fibrillation without suffering serious, long-term organ damage or dying. 

People suffering from VF need to be treated with a defibrillator to jolt the heart back into a normal rhythm. CPR (cardiopulmonary resuscitation) also helps by providing oxygen to the lungs and brain while the heart is not pumping. CPR should be given until emergency help arrives and a defibrillator is used. If treatment is not given in time, the heart will completely stop (cardiac arrest) and sudden cardiac death will result.

Although estimates vary widely, VF is considered the leading cause of sudden cardiac death in the United States. In most of those cases, the person suffers from coronary artery disease that may or not have already resulted in a heart attack. In many cases, VF occurs with 48 hours of a heart attack. However, VF leading to sudden cardiac death can also be caused by other forms of heart disease, including cardiomyopathy, myocarditis, arrhythmogenic right ventricular dysplasia and various forms of congenital heart disease. The National Institutes of Health estimates that sudden cardiac death affects nearly 300,000 people each year in the United States.

Despite its name, sudden cardiac death may not always be fatal if help can be rendered immediately. In recent years, survival rates have improved as the use of bystander CPR has increased and the time between collapse and defibrillation has decreased. Survival rates, however, remain poor among people who suffer from sudden cardiac death outside of a hospital setting. Among those who survive, long-term medication or other therapies are usually necessary, and they remain at risk for recurrent VF and sudden cardiac death.

Two other types of arrhythmias are associated with the ventricles. Premature ventricular complex occurs when an abnormal signal from the ventricle prompts an early heartbeat. Ventricular tachycardia is a fast heartbeat caused by electrical signals that begin in the ventricles instead of in the atria. Ventricular tachycardia can lead to VF if left untreated.

Atrial fibrillation (AF) is also a type of arrhythmia that results in a fast and very irregular heartbeat. However, AF differs from VF. It is not life threatening and may not produce any noticeable symptoms. The only condition in which AF can result in ventricular fibrillation is when it is associated with accessory pathway (Wolf-Parkinson-White syndrome).