The animation below shows how your heart's electrical system works. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame of the animation. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.
The animation shows how the heart's internal electrical conduction system causes the heart to pump blood.
Your hearts electrical system controls all the
events that occur when your heart pumps blood. The electrical system also is
called the cardiac conduction system. If youve ever seen the heart test
called an
EKG
(electrocardiogram), youve seen a graphical picture of the electrical
activity of your heart.
Your hearts electrical system is made up of
three main parts:
The sinoatrial (SA) node located in the right
atrium of your heart
The atrioventricular (AV) node located on the
interatrial septum close to the tricuspid valve
The His-Purkinje system located along the walls
of your hearts ventricles
A heartbeat is a complicated series of events that
take place in your heart. A heartbeat is a single cycle in which your
hearts chambers relax and contract to pump blood. This cycle includes the
opening and closing of the two inlet and outlet valves of the right and left
ventricles of your heart.
Each heartbeat has two basic parts: diastole, and
atrial and ventricular systole. During diastole, the atria and ventricles of
your heart relax and begin to fill with blood. At the end of diastole, your
hearts atria contract (atrial systole), pumping blood into the
ventricles, and then begin to relax. Your hearts ventricles then contract
(ventricular systole), pumping blood out of your heart.
Each beat of your heart is set in motion by an
electrical signal from within your heart muscle. In a normal, healthy heart,
each beat begins with a signal from the SA node. This is why the SA node is
sometimes called your hearts natural pacemaker. Your pulse, or heart
rate, is the number of signals the SA node produces per minute.
The signal is generated as the two vena cavae fill
your hearts right atrium with blood from other parts of your body. The
signal spreads across the cells of your hearts right and left atria. This
signal causes the atria to contract. This action pushes blood through the open
valves from the atria into both ventricles.
The signal arrives at the AV node near the
ventricles (see red burst on picture), where it slows for an instant to allow
your hearts right and left ventricles to fill with blood. The signal is
released and moves to the His bundle located in the walls of your
hearts ventricles.
From the His bundle, the signal fibers divide into
left and right bundle branches through the Purkinje fibers that connect
directly to the cells in the walls of your hearts left and right
ventricles (see yellow on the picture). As the signal spreads across the cells
of your hearts ventricle walls, both ventricles contract, but not at
exactly the same moment. The left ventricle contracts an instant before the
right ventricle. This pushes blood through the pulmonary valve (for the right
ventricle) to your lungs, and through the aortic valve (for the left ventricle)
to the rest of your body.
As the signal passes, the walls of the ventricles
relax and await the next signal.
This process continues over and over as the atria
refill with blood and other electrical signals come from the SA node.