<prompt> MOA of Verapamil is:Inhibition of Ca2 channelInhibition of Na-t-channelInhibition of K channelBlock membrane repolarisation  <response>: Ans: A Inhibition of Ca2 channel Verapamil blocks L type Ca2 channel delays their recovery- KDT 6th517Classification of Antiarrhythmic Drugs: four classesClass 1 action is sodium channel blockadeMembrane stabilizing drugsClass 2 action is sympatholytic Drugs with this action reduce b-adrenergic activity in the heart.Class 3 action is manifest by prolongation of the APD. Most drugs with this action block the rapid component of the delayed rectifier potassium current, 1Kr.Class 4 action is blockade of the cardiac calcium current.Class IV agents act by blocking voltage-sensitive calcium channels. Class IV drugs in therapeutic use as antidysrhythmic drugs e.g. verapamil act on L-type channels. Class IV drugs slow conduction in the SA and AV nodes where action potential propagation depends on slow inward Ca2 current, slowing the heart and terminating SVT by causing partial AV block. They shorten the plateau of the action potential and reduce the force of contraction. Reduced Ca2 entry reduces after-depolarisation and thus suppresses premature ectopic beats. 