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
Rapid depolarization (phase 0) of the action potential of ventricular muscle results from opening of: 
Select and explain. 
A. Voltage-gated Ca2+ channels, B. Voltage-gated Na+ channels, C. Acetylcholine-activated K+ channels, D. Inward rectifying K+ channels
B: Voltage-gated Na+ channels
Answer: B: Voltage-gated Na+ channels 
Explanation: Ans. B. Voltage-gated Na+ channelsVoltage-gated Na+ channels are responsible for phase 0 in ventricular muscle. Voltage gated Ca2+ channels are responsible for phase 0 in nodal cells. The potassium channels mentioned do not play a role in mediating depolarization.