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    How is the heart supposed to work?

    Electrical Regulation of the Heart: Cross section of the heart showing Sinoatrial (SA) node, 4 chambers of the heart

    To better understand Atrial Fibrillation, it is best to begin by describing the normal mechanical and electrical functions of the heart. The heart is a muscle and functions primarily as a double-sided pump. The left side of the heart pumps oxygen rich blood to all parts of the body, while the right side of the heart pumps blood back to the lungs to pick up more oxygen. For this pump to operate, it needs a source of power or energy...in this case electricity.

    The heart consists of four chambers…two upper chambers called the left and the right atria and two lower chambers known as the right and left ventricles. Between these upper and lower chambers are valves which open and close to direct the flow of blood. The left ventricle performs the most work and is the strongest of the four chambers. It ejects blood into the aorta...the main pipeline which comes out of the heart supplying oxygenated blood to the entire body.

    During a normal heartbeat, an electrical impulse originates in the right atrium where the main pacemaker of the heart is located. This natural pacemaker is called the sinoatrial node (SA node). The impulse then travels to the left atrium and down the interatrial septum to the atrioventricular node (AV node). This is the secondary pacemaker to the heart.

    The AV node slows down these impulses while they continue travelling down a common pathway branching off into the right and left bundle-branches and eventually to the ventricles. This cycle is known as normal sinus rhythm (NSR), which describes a well synchronized pumping action between the upper and the lower chambers producing the familiar (lub-dub) heart sounds.