An electrical stimulus is generated
in a special part of the heart muscle called the sinus node. It's also called the
sinoatrial node (SA node). The sinus node is a small mass of special tissue in the
upper chamber of the heart (right atrium). In an adult, the sinus node sends out a
regular electrical pulse 60 to 100 times per minute. This electrical pulse travels
through the conduction pathways and causes the heart's lower chambers (ventricles)
contract and pump out blood. The right and left atria are stimulated first and contract
to push blood from the atria into the ventricles. The ventricles then contract to
blood out into the blood vessels of the body.
The original electrical impulse
travels from the sinus node across the cells of your heart's right and left atria.
signal travels to the AV node (atrioventricular node). This node is located between
atria and the ventricles. In the AV node, the impulses are slowed down for a very
period. This allows the atria to contract a fraction of a second before the ventricles.
The blood from the atria empties into the ventricles before the ventricles contract.
After passing through the AV node, the electrical current then continues down the
conduction pathway, through a pathway called the bundle of His, and into the ventricles.
The bundle of His divides into right and left pathways (bundle branches) to give
electrical stimulation to the right and left ventricles.
Normally at rest, the heart
contracts about 60 to 100 times a minute depending on your age. In general, your heart
rate slows as you age.