Both atrial fibrillation (AFib) and ventricular fibrillation (VFib) are cardiac arrhythmias. Afib affects the atria – the upper part of your heart. VFib affects the lower part – the ventricles.

Healthy hearts contract in a synchronized way. Electrical signals in the heart cause each of its parts to work together. In both atrial fibrillation (AFib) and ventricular fibrillation (VFib), the electrical signals in the heart muscle become chaotic. This results in the inability of the heart to contract.

In AFib, the heart’s rate and rhythm will become irregular. Although serious, AFib is not typically an immediately life threatening event. In VFib, the heart will no longer pump blood. VFib is a medical emergency that will lead to death if not treated promptly.

The heart is one large organ comprised of four chambers. The parts of the heart where the fibrillation occurs determine the condition’s name. Atrial fibrillation occurs in the heart’s upper two chambers, also known as the atria. Ventricular fibrillation occurs in the heart’s lower two chambers, known as the ventricles.

If an irregular heartbeat (arrhythmia) occurs in the atria, the word “atrial” will precede the type of arrhythmia. If an arrhythmia occurs in the ventricles, the word “ventricular” will precede the type of arrhythmia.

Though they have similar names and both occur in the heart, AFib and VFib affect the body in different ways. Learn more in the following sections about how each condition affects the heart.

In a healthy heart, blood is pumped from the upper chamber into the lower chamber (or from the atria into the ventricles) in a single heartbeat. During that same beat, the blood is pumped from the ventricles into the body. However, when AFib affects a heart, the upper chambers no longer pump the blood into the lower chambers and it has to flow passively. With AFib, blood in the atria may not completely empty.

AFib is typically not life-threatening. However, it’s a serious medical condition that can lead to life-threatening complications if it goes untreated. The most serious complications are stroke, heart attack, and blockage of blood vessels leading to organs or limbs. When blood doesn’t completely empty from the atria, it can begin to pool. Pooled blood can clot, and these clots are what cause strokes and limb or organ damage when they’re ejected from the ventricles into the circulation.

Learn more: Stroke symptoms »

Ventricular fibrillation is disorderly and irregular electrical activity in the heart’s ventricles. The ventricles, in turn, do not contract and pump blood out of the heart into the body.

VFib is an emergency situation. If you develop VFib, your body will not receive the blood it needs because your heart is no longer pumping. Untreated VFib results in sudden death.

The only way to correct a heart that is experiencing VFib is to give it an electrical shock with a defibrillator. If the shock is administered in time, a defibrillator can revert the heart back to a normal, healthy rhythm.

If you have had VFib more than once or if you have a heart condition that puts you at high risk for developing VFib, your doctor may suggest you get an implantable cardioverter defibrillator (ICD). An ICD is implanted in your chest wall and has electrical leads that are connected to your heart. From there, it constantly monitors your heart’s electrical activities. If it detects an irregular heart rate or rhythm, it sends out a quick shock in order to return the heart to a normal pattern.

Not treating VFib is not an option. A Swedish study from 2000 reported the overall 1-month survival rate for patients with VFib that occurred outside of a hospital to be 9.5%. The survival range was between 50% with immediate treatment to 5% with a delay of 15 minutes. If not treated properly and immediately, people who survive VFib may suffer long-term damage or even enter a coma.

A heart-healthy lifestyle can help reduce your likelihood of both AFib and VFib. Regular physical activity and a diet rich in heart-healthy fats and limited in saturated and trans fats are key to keeping your heart strong for a lifetime.

Prevention tips

  • Quit smoking.
  • Avoid alcohol and excessive caffeine.
  • Reach and maintain a healthy weight.
  • Control your cholesterol.
  • Monitor and manage your blood pressure.
  • Treat conditions that can lead to cardiac issues, including obesity, sleep apnea, and diabetes.
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If you’ve been diagnosed with either AFib or VFib, work closely with your doctor to develop a treatment and lifestyle program that addresses your risk factors, history of arrhythmia, and health history. Together, you can treat both of these conditions before they become deadly.