Ventricular tachycardia is an arrhythmia that originates in the pumping chambers, or the ventricles. It is usually seen in patients who have damaged ventricular chambers, frequently in the aftermath of a heart attack or myocardial infarction. Scar tissue in the ventricles will alter many local electrical properties and set up conditions favorable to formation of a local electrical circuit. Under specific circumstances, the circuit can be activated leading to a rapid arrhythmia arising from a single spot within the pumping chambers. Because this is more rapid than the heart's natural electrical activity, it takes over the heart beat for the duration of the arrhythmia. Because it is so rapid, and is occurring in a damaged heart, and because the electrical sequence does not follow the normal pattern, the heart may not function properly or efficiently and low blood pressure may result.

In its most extreme form, ventricular tachycardia can lead to fatal consequences. This is a potentially dangerous arrhythmia that almost always requires therapy. In some patients, ventricular tachycardia may occur when there is no structural heart disease. This "idiopathic" form often arises from the right ventricle and less often from the left ventricle. These arrhythmias are less dangerous, but also often require therapy.