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
[{'content': 'Calcium channel blocker with maximum effect on conduction in hea is: \nSelect and explain. \nA. Phenylamine, B. Nifedipine, C. Diltiazem, D. Verapamil', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Verapamil is phenylalkylamine which depresses the SA node and slows AV conduction. Others are less potent. But verapamil can cause constipation It is class 4 antiarrhythmic drug REF.Essentials of Pharmacology KD Tripathi 8th ed.', 'role': 'assistant'}]