Figure 4.1.

By volume, cardiac muscle is primarily composed of cardiomyocytes, which are electrically active contractile cells. Myocytes are arranged into fibers and are electrically coupled via gap junction channels, which are preferentially localized to structures called intercalated discs located at the ends of the myocytes. Macroscopic conduction is highly anisotropic, and action potential waves travel more rapidly along fibers than in the cross-fiber directions. See also Figure 4.5, which describes the microscale geometry and equivalent circuit of a model of a linear strand of myocytes. Figure adapted with permission from www.e-heart.org.