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Heat Syncope (Fainting)

Heat syncope occurs when you faint suddenly and lose consciousness because of low blood pressure. Heat causes the blood vessels to expand (dilate), so body fluid moves into the legs by gravity, which causes low blood pressure and may result in fainting.

Symptoms that could lead to heat syncope (fainting) include:

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Heat syncope can be caused by blood pooling in the legs if you have been standing still for a long time in a hot environment. It can also be caused by vigorous physical activity for two or more hours before the fainting happens.

Your risk of developing heat syncope increases when you have not adjusted (acclimated) to a hot environment. Being dehydrated may also increase your risk for heat syncope. Recovery is rapid once you lie down in a cool environment.

Heat syncope is sometimes a symptom of a nervous system, metabolic, or cardiovascular problem that needs further medical evaluation.

By	Healthwise Staff
Primary Medical Reviewer	William H. Blahd, Jr., MD, FACEP - Emergency Medicine
Specialist Medical Reviewer	David Messenger, MD
Last Revised	July 19, 2010

WebMD Medical Reference from Healthwise

Last Updated: July 19, 2010

This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.