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An embolism is the sudden blockage of a blood vessel by a blood clot that has been brought to that location by the bloodstream. The clot, called an embolus, from the Greek word meaning plug, is a blood clot that has formed inside the circulatory system and is floating in the bloodstream. It will remain on the move until it encounters a blood vessel too small for it to fit through, where it will plug the vessel and prevent any further circulation of blood through it.

A blood clot that forms in a given location and remains there is called a thrombus, from the Greek word for clot.

An embolism is named by the location in which the clot lodges. A pulmonary embolism is an embolus that has plugged a blood vessel, usually an artery, in one of the lungs. A coronary embolism is obscuring the channel in one of the coronary arteries, which feed the heart muscle. A cerebral embolism lodges in a blood vessel in the brain and perhaps precipitates a stroke.

When an embolus plugs a blood vessel, the tissues that are bathed by the blood in the vessel will die when the blood supply is cut off. Death of tissue resulting from the lack of blood is called an infarct. If the embolism is in a coronary artery and the infarct is in the heart muscle it is a heart attack. The seriousness of the attack is determined by which vessel the clot blocks and how much of the heart muscle is infarcted.

The same situation applies to other organs. A cerebral embolism can cause brain damage and bring about a stroke. A pulmonary embolism causes damage to the lung tissue that can be serious. Any of these embolisms can be fatal and must be treated quickly.

Drugs can be given to dissolve the clot and other drugs can be taken to prevent the formation of any more clots.

What causes most emboli to form is not known. Some may form after surgery if air gets into the bloodstream.

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