B. Electrophysiological effects and classification of antiarrhythmic drugs D Class I( Na* channel blockers SV,V B IC SV.V* D Class II( B receptor blockers SV*V D Class Ill( prolongation of APD) SV,V D Class IV( Ca2*t channel blockers) Sv*, V primary action sitesClass I（Na+ channel blockers） IA SV, V* IB V IC SV, V* Class II（ receptor blockers） SV*, V Class III（prolongation of APD） SV, V Class IV（Ca2+ channel blockers） SV* , V B. Electrophysiological effects and classification of antiarrhythmic drugs * primary action sites