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    Electrical System of the Heart - Topic Overview

    What controls the timing of your heartbeat?

    Your heart's electrical system controls the timing of your heartbeat by regulating your:

    • Heart rate, which is the number of times your heart beats per minute.
    • Heart rhythm, which is the synchronized pumping action of your four heart chambers.

    Your heart's electrical system should maintain:

    • A steady heart rate of 60 to 100 beats per minute at rest. The heart's electrical system also increases this rate to meet your body's needs during physical activity and lowers it during sleep.
    • An orderly contraction of your atria and ventricles (this is called a sinus rhythm).

    See a picture of the heart and its electrical system camera.gif.

    How does the heart's electrical system work?

    Your heart muscle is made of tiny cells. Your heart's electrical system controls the timing of your heartbeat by sending an electrical signal through these cells.

    Two different types of cells in your heart enable the electrical signal to control your heartbeat:

    • Conducting cells carry your heart's electrical signal.
    • Muscle cells enable your heart's chambers to contract, an action triggered by your heart's electrical signal.

    The electrical signal travels through the network of conducting cell "pathways," which stimulates your upper chambers (atria) and lower chambers (ventricles) to contract. The signal is able to travel along these pathways by means of a complex reaction that allows each cell to activate one next to it, stimulating it to "pass along" the electrical signal in an orderly manner. As cell after cell rapidly transmits the electrical charge, the entire heart contracts in one coordinated motion, creating a heartbeat.

    The electrical signal starts in a group of cells at the top of your heart called the sinoatrial (SA) node. The signal then travels down through your heart, triggering first your two atria and then your two ventricles. In a healthy heart, the signal travels very quickly through the heart, allowing the chambers to contract in a smooth, orderly fashion.

    The heartbeat happens as follows:

    1. The SA node (called the pacemaker of the heart) sends out an electrical impulse.
    2. The upper heart chambers (atria) contract.
    3. The AV node sends an impulse into the ventricles.
    4. The lower heart chambers (ventricles) contract or pump.
    5. The SA node sends another signal to the atria to contract, which starts the cycle over again.

    This cycle of an electrical signal followed by a contraction is one heartbeat.

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