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Definition of Sinoatrial (SA) Node
The SA node initiates the electrical pacing impulse that causes the heart to contract.
In the healthy heart the electrical impulse spreads in an orderly and synchronized pattern through the two atria, causing them to contract.
The atrioventricular (av) node, a second small cluster of specialized nerve and muscle fibers located in the wall of the heart between the atria and the ventricles, picks up the impulse, amplifies it, and sends it through the ventricles to cause them to contract.
For further discussion of cardiovascular structure and function please see the overview section “The Cardiovascular System.”
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