This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
Plateau phase of ventricular muscle is d/t opening of 
Select and explain. 
A. Na+ channel, B. K+ channel, C. Ca - Na channel, D. Closure of K+ channel
C: Ca - Na channel
Answer: C: Ca - Na channel 
Explanation: Ca2+ influx through more slowly opening Ca2+ channels produces the plateau phaseThe initial depolarization is due to Na+ influx through rapidly opening Na+ channels Repolarization is due to net K+ efflux through multiple types of K+ channels