This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Pharmacology
A 60-year-old man with rheumatic mitral stenosis and atrial fibrillation is on therapy for a fast ventricular rate. While on treatment he develops a regular pulse of 64 beats/min. Which of the following is the probable drug that the patient is receiving? 
Select and explain. 
A. Verapamil, B. Digoxin, C. Carvedilol, D. Propranolol
B: Digoxin
Answer: B: Digoxin 
Explanation: Ans. (B) Digoxin(Ref: KDT 8th/e p561)Digitalis is used to control ventricular rate in atrial fibrillation. It increases the refractoriness of AV node and decreases the conduction through AV node.