A gravely serious cardiac arrhythmia in which each heartbeat is initiated from electrical activity in the ventricles (the lower heart chambers) rather than from the sinoatrial node in the right atrium (upper heart chamber).
It is an abnormally fast heart rate due to serious heart disease, such as myocardial infarction (heart attack) or cardiomyopathy (disease of the heart muscle). It can last for a few minutes or for several days.
Diagnosis is confirmed by ECG. Emergency treatment is with defibrillation (administration of an electric shock to the heart) and antiarrhythmic drugs taken.