• The Heart House


"Syncope" is the medical term for passing out, fainting, or losing consciousness - all are synonymous. There are several reasons for a patient to experience syncope. 

Some reasons may be related to the heart (i.e., the heart is the primary cause). Other reasons are unrelated to the heart (i.e., secondary causes). 

  • Primary, or heart-related causes of syncope include changes in one's heart rhythm (arrhythmias), problems with the heart valves, or problems with the heart muscle itself (i.e., cardiomyopathy).
  • Secondary causes of syncope include vasovagal syncope, postural orthostatic tachycardia syndrome / autonomic dysfunction ("dysautonomia"), and rarely, seizures.

Secondary Causes

Vasovagal Syncope

The nervous system and heart are in constant communication. The nervous system is responsible for instructing the heart to react appropriately to meet the body's ever-changing needs. There are signals continuously sent between the nervous system and heart, some of which will stimulate the heart while others will inhibit the heart - the end result depends on the balance between the stimulatory and inhibitory signals. In vasovagal syncope, the signal that normally inhibits the heart (i.e., from the vagus nerve) is more pronounced, resulting in a drop in blood pressure and subsequently, less blood flow to the brain.

For instance, when standing up from a seated position, the nervous system (i.e., the brain) must tell the heart to provide enough blood to our brain and muscles to allow us to stand up. The heart can accomplish this by either pumping blood more forcefully (i.e., maintaining enough blood pressure) or by beating faster. Sometimes, however, some trigger offsets the balance between the stimulatory and inhibitory signals to the heart. Examples of such triggers include being frightened/startled, the sight of blood, sitting up or standing up too quickly. When the heart gets too strong of an inhibitory signal, the heart cannot pump enough blood to the brain and muscles, potentially resulting in the person feeling either feeling faint or losing consciousness.

Prior to fainting, patients usually complain of feeling dizzy, light-headed, losing balance, then start to feel their heart racing and may have cold sweating. Things then start to look dimmer and narrower like a tunnel, and then all of a sudden the person blacks out and falls down. Bystanders usually describe the patient as looking pale, or lost his color.

Postural orthostatic tachycardia syndrome (POTS) / Autonomic Dysfunction (ie, Dysautonomia):

POTS specifically refers to the compensatory responses that occur within the cardiovascular system in response 

Almost fainted! (Pre-syncope)

Some people complain of feeling dizzy, un-steady, and getting out of balance, but do not loss consciousness, this is called near-fainting or "pre-syncope."


Click the tour bus to learn about blood circulation to the brain by looking at a simple plumbing arrangement in a town we call the Alert Village.

Click "Next" to move on to the next Common Problem.

Quick Links

Contact Us

Children's Heart Institute

P. O. Box 10066 McLean, VA 22102

Central Registration (patient appointments):

phone - 703-481-5801

Billing Inquiries:

phone - 571-612-2600 /  fax - 571-266-4096