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The Cardiac Electrical System - How the Heart Beats

By , About.com Guide

Updated: September 25, 2007

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The Cardiac Electrical Signal Spreads Across the Atria

Electrical system 2

Figure 2 - Spreading across the atria

Figure 2: The electrical impulse originates in the sinus node. From there, it spreads across both atria, causing the atria to contract. As the electrical impulse passes through the atria, it generates the so-called "P" wave on the ECG. (The P wave is indicated by the solid purple line on the ECG below.)

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