Note: Your progress in watching these videos WILL NOT be tracked. These training videos are the same videos you will experience when you take the full ProACLS program. You may begin the training for free at any time to start officially tracking your progress toward your certificate of completion.

Ventricular fibrillation (also called VFib or VF) is caused by multiple ectopic electrical impulses which depolarize the myocardium in a chaotic fashion. This results in a quivering (or fibrillatory) heart that cannot produce a pulse or adequate cardiac output.

In this lesson, we'll dig a little deeper into ventricular fibrillation and then look at a typical ECG readout for a patient in VFib and provide a cardiac interpretation. And at the end of the lesson, we'll provide a preview of the medications we'll be looking at in the following section of your ProACLS course.

Now let's take a look at an ECG for a patient in ventricular fibrillation.

Ventricular Fibrillation ECG
*Ventricular Fibrillation ECG for Adult Patient

1. The Heart Rhythm

The first thing you'll want to look at is the heart rhythm. Does the heart rhythm look regular? Or does it look irregular? In the ECG above, the rhythm is irregular.

2. The Heart Rate

Next, you'll want to look at the heart rate of the patient. What is the patient's heart rate? Is it normal? Or is it too slow or too fast? In this case, it's somewhere between 200 and 250 beats per minute and thus, extremely fast.

3. P-Wave

After looking at the heart rate, check to see if the patient's P-waves look normal by asking yourself the following few questions.

  • Are the patient's P-waves present? No.
  • Do they occur regularly? No.
  • Is there one P-wave for each QRS complex? No.
  • Are the P-waves smooth, rounded, and upright? No, only fibrillatory waves are present.
  • Do all the P-waves have a similar shape? Again, that answer is no, because normal P-waves aren't present.

4. PR Interval

Next, look at the PR interval on the patient's ECG readout and ask yourself the following questions:

  • Is the PR interval normal, meaning between .12 and .20 seconds or is it contained within one large square on the readout? The answer is no, because there isn't a PR interval.
  • Is the PR interval constant? Again, this in non-applicable since there isn't a P-wave.

5. QRS Complex

The last thing you should look at to determine if the sinus rhythm is normal or not is the QRS complex and ask yourself these questions while you do:

  • Is the QRS interval less than .12 seconds? No. In fact, there is no evidence of a QRS complex.
  • Is the QRS complex wide or narrow? Not applicable.
  • Are the QRS complexes similar in appearance or are there noticeable differences? Not applicable, since not present.

So, what is your cardiac interpretation? Based on these questions and on the findings from the ECG readout above, it would appear that this patient is in ventricular fibrillation.

  1. We have an irregular rhythm.
  2. We have no heart rate and no pulse.
  3. The P-waves are missing; there are only fibrillatory waves present.
  4. There is no PR interval.
  5. The QRS is nonexistent.

When a patient is in ventricular fibrillation, the heart has no organized rhythm as well as no coordinated contractions. The electrical activity is very chaotic. The heart quivers and it does not pump blood. Therefore, pulses are not palpable. Ventricular fibrillation may be preceded by a brief period of ventricular tachycardia with or without a pulse.

Pro Tip: VFib is a non-perfusing and lethal dysrhythmia that is most commonly seen during the first few minutes of cardiac arrest. Because of this, it's important that high-quality CPR be administered as soon as possible, including defibrillation, to increase that patient's chance of a successful resuscitation.

A Word About Pharmacology (A Preview)

It's important that you know basic information about medications and other interventions used in the ACLS algorithms. A basic understanding of pharmacology information includes the indications, contraindications, and methods of administration for each. You'll also need to know when to use which drug based on each clinical situation.

Medications and interventions that we'll be looking at in detail in the upcoming ProACLS course section are:


Adenosine is a prescription drug used for conversion to sinus rhythm of paroxysmal supraventricular tachycardia (PVST), including that associated with accessory bypass tracts (Wolff-Parkinson-White Syndrome).

Adenosine is available under the following different brand names: Adenocard, and Adenoscan.


Amiodarone is used to treat certain types of serious (possibly fatal) irregular heartbeat (such as persistent ventricular fibrillation/tachycardia). It is used to restore normal heart rhythm and maintain a regular, steady heartbeat.

Amiodarone is known as an anti-arrhythmic drug. It works by blocking certain electrical signals in the heart that can cause an irregular heartbeat.


Aspirin, also known as acetylsalicylic acid (or ASA), is a medication used to treat pain, fever, or inflammation. Specific inflammatory conditions which aspirin is used to treat include Kawasaki disease, pericarditis, and rheumatic fever.

Aspirin can also be given shortly after a heart attack to decrease the risk of death. And it can be used long-term to help prevent future heart attacks, ischemic strokes, and blood clots in people with a higher than normal risk.


Atropine is a medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate and to decrease saliva production during surgery. It is typically given intravenously or by injection into a muscle.


Dopamine is indicated for the correction of hemodynamic imbalances present in the shock syndrome due to myocardial infarction, trauma, endotoxic septicemia, open-heart surgery, renal failure, and chronic cardiac decompensation as in congestive failure.


Adrenaline, also known as epinephrine, is a hormone and medication. Adrenaline is normally produced by both the adrenal glands and a small number of neurons in the medulla oblongata where it acts as a neurotransmitter involved in regulating visceral functions.

It's used in emergencies to treat very serious allergic reactions to insect stings/bites, foods, drugs, or other substances. Epinephrine acts quickly to improve breathing, stimulate the heart, raise a dropping blood pressure, reverse hives, and reduce swelling of the face, lips, and throat.

Fibrinolytic Agents

Thrombolytic drugs, or fibrinolytic agents, are used to help dissolve blood clots. Blood clots can occur in any vascular bed. However, when they occur in coronary, cerebral, or pulmonary vessels, they can be immediately life-threatening.

Coronary thrombi are the cause of myocardial infarctions. Cerebrovascular thrombi produce strokes. And pulmonary thromboemboli can lead to respiratory and cardiac failure.


Lidocaine is used to relieve nerve pain after shingles (infection with the herpes zoster virus). This type of pain is called post-herpetic neuralgia. Lidocaine helps to reduce sharp/burning/aching pain as well as discomfort caused by skin areas that are overly sensitive to touch. Lidocaine belongs to a class of drugs known as local anesthetics. It works by causing a temporary loss of feeling in the area where you apply the patch.

Lidocaine is available under the following different brand names: Lidocaine CV, and Lidopen.

Magnesium Sulfate

Magnesium sulfate is a naturally occurring mineral used to control low blood levels of magnesium. Magnesium sulfate injection is also used for pediatric acute nephritis and to prevent seizures in severe pre-eclampsia, eclampsia, or toxemia of pregnancy.

Magnesium sulfate is available under the following different brand names: MgSO4.


Morphine is a pain medication of the opiate family which is found naturally in a number of plants and animals. It acts directly on the central nervous system to decrease feelings of pain.

Morphine can be taken for both acute pain and chronic pain. It's frequently given for pain stemming from myocardial infarction and also during labor. And it can be administered a number of different ways, including by mouth, by injection, intravenously, and rectally.


Nitroglycerin belongs to the group of medicines called nitrates. It works by relaxing the blood vessels and increasing the supply of blood and oxygen to the heart while reducing its workload.

Nitroglycerin is often used to prevent angina that's caused by coronary artery disease. And it can be used to relieve an angina attack that's already occurring.


Oxygen is the odorless gas that is present in the air and necessary to maintain life. Oxygen may be given in a medical setting, either to reduce the volume of other gases in the blood or as a vehicle for delivering anesthetics in gas form. It can be delivered via nasal tubes, an oxygen mask, or an oxygen tent. Patients with lung disease or damage may need to use portable oxygen devices on a temporary or permanent basis.


Pronestyl (procainamide hydrochloride) is a cardiac antiarrhythmic drug used to help keep the heart beating normally in people with certain heart rhythm disorders of the ventricles (the lower chambers of the heart that allow blood to flow out of the heart).

The brand name Pronestyl is discontinued in the U.S. Generic versions may be available.