This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
Inward flow of Na+ in heart leads to 
Select and explain. 
A. Plateau phase, B. Action potential, C. Repolarization, D. No Change
B: Action potential
Answer: B: Action potential 
Explanation: Ans. (b) Action potential(Ref: Ganong, 25th ed/p.521)To be more precise, influx of sodium ions causes depolarization of ventricular action potential. It is usually seen in the form of a rapid upstroke (spike)