The heart has an electrical system that controls how it beats and
pumps blood throughout the body. The electrical system controls the four
chambers of the heart. These chambers contract and relax in a specific sequence
so that blood is pumped in and out of the heart.
The heart has two upper chambers, called atria. The heart's two
lower chambers are called ventricles. These chambers are controlled by an
electrical system that generates rhythmic impulses. These impulses cause the
heart muscle around the atria and ventricles to contract or pump in a specific
sequence. The rhythm of the contractions pumps blood through the heart to the
lungs and body.
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The electrical impulses begin in or pass through small areas of
muscle cells called nodes. The impulses travel from the nodes through the heart
muscle fibers along electrical pathways. See a picture of the
conduction system of the heart.
Two nodes create these electrical impulses in the heart. They are
called the sinoatrial (sinus or SA) node and the atrioventricular (AV) node.
They control the heart's electrical system by acting together in a rhythm. You
recognize this rhythm as your heartbeat. The rhythmic cycle happens as
The SA node (called the pacemaker of the heart) sends out an
The upper heart chambers (atria) contract.
The AV node sends an impulse into the ventricles.
lower heart chambers (ventricles) contract or pump.
The SA node
sends another signal to the atria to contract, which starts the cycle over
This cycle of an electrical signal followed by a contraction is one
heartbeat. A normal heart rate for an adult is between 60 and 100 beats each
If the electrical pathway in your heart is disturbed, you can have an
abnormal heartbeat (arrhythmia). An arrhythmia may happen when the heart beats
too fast, too slow, or out of rhythm.
Primary Medical Reviewer
E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer
Rakesh K. Pai, MD, FACC
June 2, 2011
WebMD Medical Reference from Healthwise
June 02, 2011
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