This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
[{'content': 'The myocardial contraction is stimulated by \nSelect and explain. \nA. Influx of Ca++ ions, B. Influx of Na ions, C. Efflux of K ions, D. Efflux of Na ions', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The initial depolarisation is due to Na+ influx through rapidly opening Na+channels. 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.', 'role': 'assistant'}]