A conceptual model of cardiac membrane fast sodium and slow calcium ion channels: at rest (A), during the initial phases of the fast-response (B and C), and the slow-response action potentials (D and E). Activation gates are labeled “m” and “d.” Inactivation gates are labeled “h” and “f.” Source: Chapter 2. Characteristics of Cardiac Muscle Cells, Cardiovascular Physiology, 8e Citation: Mohrman DE, Heller L. Cardiovascular Physiology, 8e; 2014 Available at: http://accesscardiology.mhmedical.com/DownloadImage.aspx?image=/data/books/mohr8/mohr8_c002f003.png&sec=48779843&BookID=843&ChapterSecID=48779650&imagename= Accessed: November 07, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved