The heart has its own natural pacemaker called the sino-atrial (SA) node that maintains a normal heart rhythm and pulse rate.
As shown in the illustration, the SA node sends an electrical signal from the right atrium toward the left atrium and the two main pumping chambers, the right and left ventricles. This signal is coordinated by other groups of specialised muscle fibres called the AV
node and the bundle of His. The normal heart rate typically varies from 60 to 80 beats per minute.
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