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: Pharmacology
Quinidine exes its action on the hea 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: It is d-isomer quinidine is used as an antiarrhythmic drug. Quinidine blocks myocardial Na channels. Class 1a group of drugs- quinidine, procainamide, disopyramide Ib: Lidocaine, phenytoin Ic-encainide, flecainide Ref: KD tripathi 8th ed.