Antagonist--Ca2+ Channel-Semotiadil. Semotiadil fumarate {( + )-(R)-32-[5-methoxy-2-[3-[methy1[2-[3,4-(methylenedioxy)phenoxy]-ethyl]amino]propoxy]phenyl-W-1,4-benzothiazin-3(4H)-one hydrogen fumarate, or SD-321 l}, shown in Fig. 1, is a novel Ca2+ antagonist with a benzothiazine ring (8,26). Semotiadil exerts potent and long-lasting Ca'+ antagonistic actions, as shown by the results of in vitro and in vivo experiments. Semotiadil had intermediate tissue selectivities:it is more vasoselective than diltiazem and verapamil and more cardioselective than nifedipine. Semotiadil has been called a "second generation of