Semotiadil (also known as sesamodil or SD 3211) is a (+)-(R)-stereoisomer, the corresponding (−)-(S)-stereoisomer is called levosemotiadil. Semotiadil, a benzothiazine derivative was developed as a novel Ca2+ channel blocker with antiplatelet activity. Experiments on rodents have revealed that the drug had an advantage in the treatment of angina with regard to long-lasting action and selectivity for coronary artery and myocardium. In addition, semotiadil improved survival of rats with monocrotaline-induced pulmonary hypertension: comparison with diltiazem. Semotiadil was studied in phase II clinical trials for the treatment of angina pectoris and hypertension in Europe, and in Japan for the treatment of arrhythmias. However, the further development of semotiadil has now been discontinued.