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Fainting is the sudden loss of consciousness.


In general, fainting is caused by decreased blood flow to the brain.

Blood Flow to the Brain

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This can occur due to:

  • Vasovagal spells (most common cause)—simple fainting that can occur:
    • During medical procedures
    • During times of high stress, trauma, or fright
    • After standing still for a long period of time
  • Low blood pressure, especially when standing (called orthostatic hypotension)
  • Dehydration
  • Anemia due to blood loss
  • Side effect of a medication
  • Seizure
  • Stroke or transient ischemic attack
  • Too rapid or too slow heart rhythm, abnormal rhythm
  • Organic heart problems such as:
    • Hypertrophic cardiomyopathy
    • Pulmonary stenosis
    • Constrictive pericarditis

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

  • Heart disease, especially congestive heart failure or abnormal rhythms
  • Blood loss
  • Medications, including:
    • Blood pressure medications
    • Drugs that enlarge blood vessels
    • Drugs that regulate the heart's rhythm
    • Water pills (diuretics)


Symptoms include:

  • Sudden loss of consciousness
  • Inability to remain standing or sitting
  • Consciousness regained without any need for intervention
  • Dizziness or lightheadedness before losing consciousness


The doctor will ask about your symptoms and medical history, and perform a physical exam.

Tests may include (in order of importance):

  • Blood tests—to look for anemia, hypoglycemia, low potassium, and low magnesium
  • Electrocardiogram (EKG)—a test that records the heart's activity by measuring electrical currents through the heart muscle
  • Holter monitoring—a mobile EKG test that is performed over 24 hours while you go about your usual daily activities
  • Head CT scan—a type of x-ray that uses a computer to make pictures of the brain
  • Electroencephalogram (EEG)—a test that records the brain's activity by measuring electrical currents through the brain
  • MRI scan of the brain—a test that uses magnetic waves to make pictures of the brain
  • Echocardiogram—a test that uses high-frequency sound waves (ultrasound) to examine the size, shape, and motion of the heart
  • Tilt table testing—a tilted table that is used to provoke syncopal symptoms (medication may be used)
  • Cardiac catheterization—a tube-like instrument inserted into the heart through a vein or artery (usually in the arm or leg) to detect problems with the heart and its blood supply


Treatment will depend on the underlying condition that has caused fainting. For example:

  • Abnormal heart rhythms can be treated with medications or by implanting a pacemaker.
  • If a medication is causing syncope, it may need to be changed or discontinued.
  • Anemia or other blood abnormalities should be treated.


If you feel any warning signs, such as dizziness or lightheadedness, sit or lie down immediately so that you don't get hurt falling during a fainting spell.

In a recent randomized trial involving 223 patients with vasovagal syncope, training to perform certain maneuvers during warning signs of an impending spell reduced the risk of recurrent symptoms. These physical counterpressure maneuvers, designed to rapidly raise blood pressure and increase blood flow to the brain, included: *

  • Crossing the legs while tensing the muscles of the legs, abdomen, and buttocks
  • Forcefully squeezing a rubber ball or any other available object as hard as possible in the dominant hand
  • Gripping one hand with the other while tensing both arms and raising the elbows slightly

If you are prone to fainting:

  • Get up slowly and carefully from lying down. Start by sitting up. Don't ever jump to a standing position.
  • Ask your doctor if you should be on a high-salt diet.
  • Drink lots of fluids.


American Heart Association

Columbia University Medical Center


Alberta Health and Wellness

BC Health Guide


Cecil Textbook of Medicine . 21st ed. WB Saunders Company; 2000.

Griffith's 5-Minute Clinical Consult . Lippincott, Williams, and Wilkins; 2001.

TH Miller and JE Kruse. Evaluation of syncope. Am Fam Physician. 2005;72:1492-1500.

Updated Treatment section on 2/6/2007 according to the following study, as cited by DynaMed's Systematic Literature Surveillance : van Dijk N, Quartieri F, Blanc JJ, et al. Effectiveness of physical counterpressure maneuvers in preventing vasovagal syncope: the Physical Counterpressure Manoeuvres Trial (PC-Trial). J Am Coll Cardiol. 2006;48:1652-1657.

Last reviewed November 2007 by Kari L. Kassir, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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