How Do You Know if You Have Atrial Fibrillation (AFib)?

Ask a Doctor

I have an overactive thyroid, which I control with medication. The problem is, sometimes I feel as if my heartbeat is speeding up and I get lightheaded. This usually happens in social situations, so I don’t know whether to attribute it to anxiety, medication side effects, or atrial fibrillation. I know AFib is one of the symptoms that can result from a hyperactive thyroid, so how do you know if you have AFib?

Doctor's Response

Not all heart palpitations are atrial fibrillation, but a continuing feeling of heart fluttering in the chest together with a fast or slow pulse should be evaluated by a doctor or at a hospital emergency department. For example, you could be having atrial flutter (rapid, regular electrical impulses of about 250-300 impulses per minute from the atrial tissue causing a rapid ventricular response [rvr] or rapid heartbeat) or a sinus tachycardia.

Individuals should call for treatment within 24 hours if they have atrial fibrillation that comes and goes, have previously been evaluated and treated, and are not experiencing chest pain, shortness of breath, weakness, or fainting.

Patients should call their doctor or cardiologist if they have persistent atrial fibrillation while on medical therapy for the condition if symptoms worsen or new symptoms such as fatigue or mild shortness of breath occur.

Patients should call their doctor or pharmacist if they have questions about medications and dosages.

Call 9-1-1 for emergency medical services when atrial fibrillation occurs with any of the following:

  • Severe shortness of breath
  • Chest pain
  • Fainting or light headedness
  • Weakness
  • Very rapid heartbeat or palpitations
  • Low blood pressure
Symptoms of atrial fibrillation vary from person to person.
  • A number of people have no symptoms.
  • The most common symptom in people with intermittent atrial fibrillation is palpitations, a sensation of rapid or irregular heartbeat. This may make some people very anxious. Many people also describe an irregular fluttering sensation in their chests. This irregular fluttering sensation is due to the irregular rapid ventricular response (rvr) of the ventricles to the rapid irregular atrial electrical activity.
  • Some people become light-headed or faint.
  • Other symptoms include weakness, lack of energy or shortness of breath with effort, and chest pain or angina.
There are a few patients that have potentially life-threatening AFib symptoms that need immediate attention and intervention with electric cardioversion. The symptoms and signs are as follows:

For more information, read our full medical article on AFib.

Health Solutions From Our Sponsors

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"Heart Disease Pictures Slideshow: A Visual Guide to Heart Disease." MedicineNet. 30 Sept. 2009. <>.

Gage, Brian F., et al. "Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial Fibrillation." The Journal of the American Medical Association 285.22 (2001): 2864-2870.

Rosenthal, Lawrence, et al. "Atrial Fibrillation." Medscape. 30 Jan. 2012. <>.

Rosenthal, Lawrence, et al. "Atrial Fibrillation Medication." Medscape. 15 Mar. 2012. <>.

UpToDate. Patient information: Atrial fibrillation (Beyond the Basics).