Harvard Heart Letter

What's at the heart of fainting?

Most fainting is not related to abnormal heart rhythms.

Fainting, the temporary loss of consciousness that doctors call syncope (SINK-uh-pee), can be embarrassing, scary, and dangerous. It's also quite common — an estimated one in three people faints at least once in their lifetime.

People pass out when the brain doesn't get enough blood and becomes deprived of fuel and oxygen. This is usually caused by a sudden drop in blood pressure (hypotension).

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