What makes your heart beat?

Let’s take a closer look inside the heart. The yellow objects are not nerves. They’re actually specialized cardiac muscle cells in the walls of the heart. Their job is to send signals to the rest of the heart muscle and cause a contraction. Together, this group of cells is called the Cardiac conduction system.

The main components of the Cardiac conduction system are the SA node, AV node, Bundle of His, Bundle branches, and Purkinje fibers. Let’s follow a signal through the contraction process. The SA node starts the sequence by causing the atrial muscles to contract. That’s why doctors sometimes call it the anatomical pacemaker.

From there, the signal travels to the AV node, through the Bundle of His, down the Bundle branches, and through the Purkinje fibers, causing the ventricles to contract. This signal creates an electrical current that can be seen on a graph called an Electrocardiogram, or EKG.

Doctors us an EKG as a way of seeing how well the Cardiac conduction system works. Any changes to the EKG can mean serious problems.

Review Date:1/1/2023
Reviewed By:Michael A. Chen, MD, PhD, Associate Professor of Medicine, Division of Cardiology, Harborview Medical Center, University of Washington Medical School, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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