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
Which of the following antiarrhythmic drugs mediates its effect by interfering with movement of calcium through the slow channel? 
Select and explain. 
A. phenytoin, B. verapamil, C. lidocaine, D. amiodarone
B: verapamil
Answer: B: verapamil 
Explanation: The slow channel for calcium assumes considerable importance in the region of the sinus node and AV node. For verapamil, this results in both antiarrhythmic and negative inotropic effects. Different classes of calcium channel blockers have differential effects on these slow channels, explaining the different clinical properties of the various calcium channel blocking drugs.