Answer: The SA node
Answer choices are:
A. The AV node
B. The SA node
C. The purkinje fibers
D. The AV bundle
The SA node is the heart's natural pacemaker consisting of a cluster of cells located in the upper part of the wall of the right atrium. (the right upper chamber of the heart). The electrical impulses are produced and sent out from there to regulate heartbeat. This is also called the sinus code.