If the coronary arteries and veins are considered the plumbing of the heart, then the conduction system (shown in black below) can be considered the electrical wiring of the heart. Through this wiring, each muscle fiber of the heart knows when and how fast to beat so that the heart can pump efficiently.

The electrical system of the heart is greatly affected by the brain and by certain hormones and body chemicals called electrolytes. How these elements work with the rhythm generators of the heart determines the heart rate and sequence of the heartbeat. The sino-atrial (SA) node is the body's main natural cardiac pacemaker. The heartbeat starts here and spreads like the ripples in a pond throughout the network of conduction fibers in the two atria (the two upper chambers), causing them to contract. Normally, the heartbeat can only reach the ventricles (the two lower chambers) after it has passed through the atrioventricular (AV) node. The AV node slows down the electrical signal so that the atrial contractions can finish and fill the ventricles more completely. The AV node also prevents the lower chambers from beating too fast if the atria develops a fast rhythm (tachyarrhythmia). The electrical signal finally passes to the ventricles, the main work horses of the heart, through the bundle of His, bundle branches, and the Purkinje system (a specialized network of nerves that coordinates contraction of the ventricles). Each heartbeat is then completed and a new one is initiated in the SA node.

The heartbeat is a beautiful combination of the heart's own natural rhythms and the brain's and body's requirements for energy. When you are nervous or exercising, the heartbeat accelerates; during relaxation, it slows.

Anatomy & Physiology Anatomy & Physiology
Cardiac Contractility Cardiac Contractility
Coronary Circulation Coronary Circulation
Electrophysiology Electrophysiology
Non-Invasive Cardiology Non-Invasive Cardiology
Pacemakers Pacemakers

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