The heart is a pump made up of two upper chambers (atria) and two lower chambers (ventricles). The pump is powered by an electrical system that generates rhythmic impulses. These impulses cause the heart muscle to relax and contract in a specific sequence, pumping blood through the heart to the lungs and body.
Electrical pulses through the heart begin in or pass through small masses of muscle cells called nodes. The pulses travel from the nodes through the heart muscle fibers, causing the heart to contract or pump. Rhythmic pulses keep the heart pumping and keep blood flowing to the lungs and body.
The two nodes that create electrical impulses in the heart are called the sinoatrial (sinus or SA) node and the atrioventricular (AV) node.
The SA node is considered the pacemaker of the heart. It generates electrical signals that cause the upper heart chambers (atria) to contract. The SA node normally sends 60 to 100 impulses per minute in an adult and up to 140 beats per minute in a baby. This is called normal sinus rhythm.
Shortly after the SA node generates electrical signals in the atria, the AV node sends an impulse into the ventricles, causing them to contract or pump. A disturbance anywhere along this electrical pathway can cause an abnormal heartbeat (arrhythmia).
Credits
| Author | Shannon Erstad, MBA/MPH |
| Editor | Kathleen M. Ariss, MS |
| Associate Editor | Terrina Vail |
| Primary Medical Reviewer | Michael J. Sexton, MD - Pediatrics |
| Specialist Medical Reviewer | Larry A. Latson, MD - Pediatric Cardiology |
| Last Updated | October 27, 2005 |
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