Levosemotiadil is an S-enantiomer of semotiadil. It is an antiarrhythmic drug with sodium and calcium channel blocking action, as well as potassium blocking activity. Levosemotiadil is bound strongly and enantioselectively to human serum albumin and human alpha1-acid glycoprotein. Since levosemotiadil is hydrophobic basic drug, it is likely that this drug is also bound to lipoprotein in human plasma. Levosemotiadil might be effective in prevention of lethal arrhythmias. It was shown, that levosemotiadil prevented ventricular fibrillation in 64% of the high-risk animals. Heart rate responses to myocardial ischemia and to graded doses of isoproterenol were blunted by the high dose of levosemotiadil. Levosemotiadil had been in phase II clinical trials by Santen Pharmaceutical for the treatment of arrhythmias. However, this study was discontinued.