<prompt> The myocardial contraction is stimulated byInflux of Ca ionsInflux of Na ionsEfflux of K ionsEfflux of Na ions  <response>: The initial depolarisation is due to Na influx through rapidly opening Nachannels. The inactivation of Na channels contributes to rapid repolarization phase. Ca2 influx through more slowly opening Ca2 channels produces plateau phase, and depolarization is due to net K efflux through multiple types of K channels. Ref: Ganong;s review of medical physiology; 23rd edition; pg:491. 