This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Quinidine exerts its action on heart by: 
Select and explain. 
A. Ca2+ channel blockade, B. Na+ channel blockade, C. K+ channel opening, D. Cl– channel opening
B: Na+ channel blockade
Answer: B: Na+ channel blockade 
Explanation: None