Can someone tell me what's supraventricular tachycardia?

Rhythm disturbance: The heart normally initiates its rhythm from a tiny group of specialized cells in the right atrium called the sinus node. When the rhythm begins elsewhere in one of the atria and propagates at a rapid rate (usually 180 to 220 beats per minute), it's called a supraventricular (arising above the ventricles) tachycardia (heart rate of >100).

Arrhythmia: Supraventricular tachycardia is a general term for a group of rhythm disturbances involving the upper chambers of the heart (the atria) where the upper chambers beat abnormally fast relative to the lower pumping chambers (ventricles).