<prompt> Cardiac muscles action potential at plateau is due toInflux of NaEfflux of KInflux of caInflux of cl  <response>: Ca2 influx through more slowly opening Ca2 channels the Ca2 current, ICA produces the plateau phaseRepolarization is due to net K efflux through multiple types of K channelsThe initial depolarization is due to Na influx through rapidly opening Na channels Ref: Ganongs Review of Medical Physiology Twenty-Third Edition pg:491 