Calcium channel blocker with maximum effect on conduction in hea is:: (A) Phenylamine, (B) Nifedipine, (C) Diltiazem, (D) Verapamil
Answer is D. 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.