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: Medicine
[{'content': 'Which of the following drugs causes an increase in the effective refractory period of the atrioventricular (AV) node? \nSelect and explain. \nA. bretylium, B. amiodarone, C. procainamide, D. quinidine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Amiodarone causes a decrease in the sinus rate and an increase in the effective refractory period in the atrium, the AV node, and the ventricle. The pharmacology of amiodarone is complex and incompletely understood.', 'role': 'assistant'}]