ectopic
Heart excitation originates in the sino-atrial node.
In the Sinoatrial Node
the SA node
You may be asking about the sinoatrial node and the atrioventricular node, two nerve bundles that work together to regulate the heartbeat.
Sinatrial nODE
The normal heartbeat begins as an electrical impulse in the sino-atrial node (or SA node). The SA node is called the pacemaker of the heart. It is located in the R atrium, just below the entrance of the superior vena cava.
The S-A node
it is valves in the heart opening and closing.
sinoatrial node
The sino-atrial node (SA node) and, specifically the tissue of Bachmann's Bundle located within the SA node.
Each heartbeat begins with an action potential generated at the sinoatrial node or simple call the SAnode.
Pacemaker (sinoatrial node)