Autorhythmic cells other than those in the SA node or AV node sometimes adapt a depolarization frequency more rapid than that of the SA node, producing a premature heartbeat. Cells acting in this way are referred to as a(n) _____.

3000+ review questions on anatomy and physiology. 

Anatomy refers to the internal and external structures of the body and their physical relationships, whereas physiology refers to the study of the functions of those structures.