**     DCI Home:				 Heart & Vascular Diseases:				How the Heart Works: Electrical System      What Is ...AnatomyContractionCirculationElectrical SystemHeart								Disease  Your Heart’s Electrical System
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. 
The animation shows how the heart's internal electrical conduction system causes the heart to pump blood. 

Your heart’s electrical system controls all the								  events that occur when your heart pumps blood. The electrical system also is								  called the cardiac conduction system. If you’ve ever seen the heart test								  called an								  EKG								  (electrocardiogram), you’ve seen a graphical picture of the electrical								  activity of your heart.

Your heart’s 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 heart’s ventricles

A heartbeat is a complicated series of events that								  take place in your heart. A heartbeat is a single cycle in which your								  heart’s 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								  heart’s atria contract (atrial systole), pumping blood into the								  ventricles, and then begin to relax. Your heart’s 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 heart’s 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 heart’s right atrium with blood from other parts of your body. The								  signal spreads across the cells of your heart’s 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 heart’s right and left ventricles to fill with blood. The signal is								  released and moves to the His bundle located in the walls of your								  heart’s 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 heart’s left and right								  ventricles (see yellow on the picture). As the signal spreads across the cells								  of your heart’s 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.
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