Ventricular tachycardia is an abnormally fast heart rate. The abnormal heart rate originates in one of the heart's lower chambers (ventricles). It is diagnosed when there are three or more beats in succession originating from a ventricle. The heart beats at a rate greater than 100 beats per minute, but less than 200 beats per minute.

Ventricular tachycardia is considered sustained if it lasts more than 30 seconds. When this condition is sustained, the ventricles are not able to fill with enough blood for the heart to keep blood flowing properly through the body. This can result in lowered blood pressure, heart failure, and death.

Heart Chambers and Valves
heart anatomy
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Damage to the ventricles can cause ventricular tachycardia. This damage to the heart muscle may be due to conditions like heart attack or cardiomyopathy.