What is the definition or description of: Rapid beating of upper heart chambers?

Rapid Heart Beat. A Heart beat (pulse) over 100 beats per minute. The medical term is tachycardia. There are several reasons for a tachycardia. The most common is a sinus tachycardia which is usually a normal response to physical, emotional or metabolic exertion or illness. Other reasons are for rhythm problems such as atrial fibrillation, atrial flutter, supraventricular tachycardia, and others.