Atrial Fibrillation vs. Ventricular Fibrillation

Medically Reviewed by James Beckerman, MD, FACC on July 08, 2022
6 min read

Atrial fibrillation and ventricular fibrillation are both types of irregular heartbeats (arrhythmias). Atrial fibrillation (AFib) affects the two upper chambers of your heart. Ventricular fibrillation (VFib) affects the two lower chambers of the heart. As many as 6 million people in the U.S. have AFib, and the CDC says that could jump to 12 million by 2030. AFib is more common, and research has shown that AFib can triple your risk for getting VFib. VFib can be the far more dangerous of these two conditions.

Atrial fibrillation, or AFib, is an unusually fast heartbeat in the heart’s upper chambers, sometimes as many as 400 beats or more a minute. (Usually, the heart beats 60 to 150 times a minute.)

In a healthy heart, electrical signals originating in the heart’s upper chambers (the atria) tell it to beat. This causes the heart muscles to contract and move blood into the heart’s lower chambers (ventricles). More contractions push the blood from the ventricles to the rest of your body. Problems come in when these rhythms are disrupted and the heart muscles start to fibrillate (quiver).

Like AFib, VFib is an irregular heartbeat caused by an electrical malfunction. In this case, though, the problems affect the lower chambers of the heart, which can drastically reduce blood flow to the rest of the body.

AFib can cause blood to pool in the chambers, raising the risk of blood clots and strokes. People with AFib are five times more likely to have a stroke versus people who don’t have the condition. They also have a higher risk of heart failure, heart attack, cardiac arrest, and dementia.

While not as common as AFib, ventricular fibrillation is more deadly. It can cause sudden cardiac arrest or sudden cardiac death, the leading killer in the U.S.

The chaotic electrical signals in the heart trigger AFib, but experts don’t always know why these signals go wrong. Often it has to do with structural problems in the heart, like heart valve issues or heart defects you’re born with.

Heart attacks are one of the main causes of VFib. Many of the factors that can raise your risk of AFib can also increase the odds of developing VFib, including:

  • Heart disease
  • Cocaine or methamphetamine use
  • Physical stress from surgery (especially heart, lung, and esophageal surgery) or a serious illness

Other contributors to your AFib risk are:

In addition to the factors that can increase the risk for both AFib and VFib, other things can raise your risk for VFib, including:

  • Trauma to the chest, such as from a baseball or hockey puck
  • Other arrhythmias
  • Certain medications
  • Sepsis, an extreme reaction throughout your body to an infection
  • Too much or not enough potassium in your blood (called an electrolyte imbalance)

Usually, people with VFib collapse and lose consciousness (pass out) with little or no warning. It’s an emergency and help is needed right away. But you may have some signs before VFib. They are similar to AFib symptoms and, for both, can include:

Other red flags for VFib besides collapsing are:

  • Nausea
  • Cardiac arrest
  • Extreme shortness of breath

If you have AFib you can also break out sweating and have a hard time breathing, especially if you’re lying down. You may also feel very tired.

Doctors normally don’t check for AFib unless you have a risk factor. But, a regular physical exam can pick up some of the symptoms, like a fast or irregular heartbeat. To make sure, your doctor will likely perform an electrocardiogram (ECG, EKG) to look at electrical signals. They may also do:

  • An echocardiogram, which uses ultrasound to assess blood flow and muscle contractions
  • Blood tests to look for problems with potassium and thyroid hormone levels
  • Additional tests to look for hidden causes

Many of the same tools used to diagnose AFib are also used to diagnose Vfib, including an ECG or EKG and an echocardiogram, especially if you’ve had a cardiac arrest.

Other tests might include:

  • Blood tests to find enzymes that may be released after a heart attack
  • Coronary catheterization (angiogram), when dye is put into an artery to show on an X-ray whether any of your arteries are blocked
  • Cardiac CT scan to create images of your heart
  • Cardiac MRI to see your blood flow

Treating AFib

There’s no cure for AFib but there are things you can do, plus drugs and surgeries to fix your heart’s electrical rhythms, get your heart rate back to normal, and stop future blood clots and strokes.

Lifestyle changes you can make:

Medications include:

If lifestyle changes and medicine don’t control your AFib, your health care provider may suggest surgery, such as:

  • Surgical ablation to destroy sections of heart tissue responsible for the bad electrical signals
  • Maze procedures to create scar tissue in the heart that reroutes the electrical signals
  • Electrical cardioversion to shock your heart back into a normal rhythm

Treating VFib

There are two stages of treatment for VFib. The first is emergency treatment of sudden cardiac arrest with CPR and defibrillation (shocking the heart rhythm back to normal). If defibrillation happens within 3 minutes of the collapse, as many as 95% of people survive. Actual survival rates are much lower at about 20% to 35% of people who have cardiac arrest outside of the hospital.

Once the immediate crisis has been handled, doctors will prescribe treatments including medications and possibly surgery, such as:

  • Implanting a cardioverter-defibrillator (ICD), a device that delivers an electrical shock whenever an arrhythmia is detected
  • Cardiac ablation or applying extreme heat or cold to create small scars to block bad electrical signals
  • Placing a stent, to make sure a clogged artery stays open, if a heart attack caused the VFib
  • Coronary bypass surgery if blockages from coronary artery disease caused the VFib

You can take certain actions to help prevent both VFib and AFib:

  • Eat a diet high in fruits, vegetables, and whole grains but low in salts, refined sugar, and saturated fat
  • Exercise regularly
  • Stop smoking, drinking too much alcohol
  • Make sure your blood pressure and cholesterol are at healthy levels

Call a doctor or 911 if you have symptoms of AFib or VFib or if you:

  • Have signs of a stroke, such as drooping on one side of the face, trouble with vision, or slurred or strange speech
  • Have symptoms of a heart attack, including:
    • Pain in the chest, jaw, neck, back, or both arms or shoulders
    • Trouble breathing
    • Weakness or lightheadedness

Fainting suddenly can be a sign of cardiac arrest. In this case, people around you need to call 911 and start CPR. If you're at risk for AFib or VFib, make sure friends and family know what to do in an emergency and wear a medical ID bracelet.