Atrial Fibrillation (AFib) vs. Ventricular Fibrillation (VFib): What Are The Differences?

  • Medical Author:
    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

  • Medical Editor: John P. Cunha, DO, FACOEP
    John P. Cunha, DO, FACOEP

    John P. Cunha, DO, FACOEP

    John P. Cunha, DO, is a U.S. board-certified Emergency Medicine Physician. Dr. Cunha's educational background includes a BS in Biology from Rutgers, the State University of New Jersey, and a DO from the Kansas City University of Medicine and Biosciences in Kansas City, MO. He completed residency training in Emergency Medicine at Newark Beth Israel Medical Center in Newark, New Jersey.

Atrial Flutter and Atrial Fibrillation: What's the Difference?

Atrial flutter and atrial fibrillation are both types of abnormal heart rhythms, or an arrhythmia in which your heart rate is rapid, and you can feel your pulse very strongly. Both conditions can occur together or separately, and both can be dangerous if not treated. Symptoms are similar and include:

  • Fatigue
  • Shortness of breath You can feel your heart beating or pounding in your chest
  • A feeling like you're going to faint.

What does “fibrillation” mean?

Atrial fibrillation and ventricular fibrillation are heart conditions that include the term “fibrillation.” When defined as related to the heart, "fibrillation" refers to a very rapid irregular contractions of the heart’s muscle fibers.

What are the main differences between AFib and VFib?

Atrial fibrillation or AFib, and ventricular fibrillation or VFib, are both a type of abnormal heart rhythm or heartbeat called an arrhythmia.

One of the main differences between these two heart conditions is that ventricular fibrillation is life threatening if treatment isn't begun immediately, while atrial fibrillation generally is not immediately life threatening, but can cause problems with the heart function that are very dangerous if not treated effectively.

  • AFib produces irregular electrical signals in the upper chambers of the heart muscle called the atria (and may include the AV node), causing the heart’s atria to beat irregularly and usually faster than normal. AFib usually is not an immediately life-threatening abnormal heartbeat (arrhythmia).
  • VFib produces irregular electrical signals in the lower chamber heart muscles (ventricles) that are so chaotic that the heart muscles can’t pump blood effectively. This type of heart condition is life-threatening, and must be treated immediately or the patient will likely die.

What are the main similarities between these two heart conditions?

Both types of heart disease are considered to be a type of abnormal heartbeat (arrhythmia).

Both AFib and VFib can be detected by ECG’s and CPR defibrillators (machines that can identify arrhythmias and, if needed, can deliver shocks, or electrical impulses, to the heart to treat a life-threatening arrhythmia like VFib).

What are AFib and VFib, and how do they affect the heart?

To understand what AFib and VFib are, you need to know a little about your heart and how it works normally. The heart is composed of four muscular chambers; two upper and two lower. The two upper chambers are called the atria. The two lower chambers are called the ventricles.

  • The impulse is first generated at the sinoatrial node (SA node), which causes the right atrium to contract sending blood to the right ventricle.
  • The right ventricle then sends blood to the lungs to get rid of carbon dioxide (CO2) and to pick up oxygen (02).
  • The lungs then return the fresh oxygenated blood to the left atrium, which contracts to fill the left ventricle.
  • The left ventricle muscle tissue contracts, and generates the pulse and sends fresh oxygenated blood under pressure (blood pressure) to your body’s organs.
  • Each heartbeat repeats the process, and normally produces an electrical signal that is consistent for each heartbeat. When the electrical signal is irregular in any way, the patient has an abnormal heart rhythm.

Picture of a Cross Section of the Heart Including the Atria and Ventricles.
Picture of a Cross Section of the Heart Including the Atria and Ventricles.

AFib and VFib are both termed arrhythmias (abnormal heart rhythms). AFib is a type of arrhythmia termed supraventricular tachycardia, meaning that the problem occurs above the ventricles. For AFib, the abnormal heart rhythms are due to irregular electrical activity in the atria, mainly the right atrium. It usually results in a fast and irregular heartbeat.

Picture of the Electrical Activity of the Heart During Atrial Fibrillation
Picture of the Electrical Activity of the Heart During Atrial Fibrillation

In contrast, VFib occurs when the electrical signal is chaotic within the ventricular muscular tissue and results in no effective heartbeat so there is no effective blood pressure or pulse generated, which results in sudden cardiac death of the individual if the abnormal heartbeat continues and is not treated immediately (emergently).

Medically Reviewed by a Doctor on 5/10/2017

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