Ventricular tachycardia (V-tach) is a type of abnormal heartbeat (arrhythmia) that starts in the lower chambers of the heart, the ventricles. Tachycardia, a fast heart rate, usually occurs when the electrical signals in your heart are sent too quickly. This keeps your heart from pumping enough blood and oxygen through your body. Most people with ventricular tachycardia have a heart rate of at least 170 beats per minute.