Electrical conduction in heart.
Illustration of a human heart, showing the specialised tissue that conducts the electrical signals governing heart- beats. The heartbeat starts in the heart's natural pacemaker, the sinoatrial (SA) node (green). This small area of specialised muscle cells emits an electrical impulse about 70 times a minute. The impulse spreads through the muscles of the atria (upper heart chambers), making them contract, and is carried via special fibres to the atrioventricular (AV) node (orange). The AV node delays the impulse to allow the ventricles (lower heart chambers) to fill, before effecting ventricular contraction via branches of the bundle of HIS (red).
Did you know that our heart has an electrical system? It is a bit like the electrical wiring in our home. The heart's electrical system creates the signals that tell our heart when to beat. And our heartbeat is what pumps blood throughout our body. The heart's electrical system is also called the cardiac conduction system.
The electrical impulse leaves the SA node and travels to the right and left atria, causing them to contract together. This takes 0.04 seconds. There is now a natural delay to allow the atria to contract and the ventricles to fill up with blood.
The electrical impulse has now traveled to the atrioventricular node (AV node). The electrical impulse now goes to the Bundle of His, then it divides into the right and left bundle branches where it rapidly spreads using Purkinje fibers to the muscles of the right and left ventricle, causing them to contract at the same time.
Any of the electrical tissue in the heart has the ability to be a pacemaker. However, the SA node generates an electric impulse faster than the other tissue so it is normally in control. If the SA node fail, the other parts of the electrical system can take over, although usually at a slower rate.
The S-A node normally produces 60-100 electrical signals per minute — this is your heart rate, or pulse. With each pulse, signals from the S-A node follow a natural electrical pathway through your heart walls. The movement of the electrical signals causes your heart's chambers to contract and relax. In a healthy heart, the chambers contract and relax in a coordinated way, or in rhythm. When your heart beats in rhythm at a normal rate, it is called sinus rhythm.