Electrical System of the Heart - Topic Overview
AV node and ventricles
After the electrical signal has caused your atria to contract and
pump blood into your ventricles, the electrical signal arrives at a group of
cells at the bottom of the right atrium called the atrioventricular node, or AV
node. The AV node briefly slows down the electrical signal, giving the
ventricles time to receive the blood from the atria. The electrical signal then
moves on to trigger your ventricles.
When the electrical signal leaves the AV node, it triggers the
- The signal travels down a bundle of conduction
cells called the bundle of His, which divides the signal into two branches: one
branch goes to the left ventricle, another to the right
- These two main branches divide further into a system of
conducting fibers that spreads the signal through your left and right
ventricles, causing the ventricles to contract.
- When the ventricles
contract, your right ventricle pumps blood to your lungs and the left ventricle
pumps blood to the rest of your body.
After your atria and ventricles contract, each part of the system
electrically resets itself.
How does the heart's electrical system regulate your heart rate?
The cells of the SA node at the top of the heart are known as the
pacemaker of the heart because the rate at which these cells send out
electrical signals determines the rate at which the entire heart beats (heart
The normal heart rate at rest ranges between 60 and 100 beats per
minute. Your heart rate can adjust higher or lower to meet your body's needs.
What makes your heart rate speed up or slow down?
Your brain and other parts of your body send signals to stimulate
your heart to beat either at a faster or a slower rate. Although the way all of
the chemical signals interact to affect your heart rate is complex, the net
result is that these signals tell the SA node to fire charges at either a
faster or slower pace, resulting in a faster or a slower heart rate.
For example, during periods of exercise, when the body requires
more oxygen to function, signals from your body cause your heart rate to
increase significantly to deliver more blood (and therefore more oxygen) to the
body. Your heart rate can increase beyond 100 beats per minute to meet your
body's increased needs during physical exertion.
Similarly, during periods of rest or sleep, when the body needs
less oxygen, the heart rate decreases. Some athletes actually may have normal
heart rates well below 60 because their hearts are very efficient and don't
need to beat as fast. Changes in your heart rate, therefore, are a normal part
of your heart's effort to meet the needs of your body.