(S)-(+)-Dimethindene maleate, an enantiomer, is a potent M 2 -selective muscarinic receptor antagonist ( pA 2 = 7.86/7.74; pK i = 7.78). (S)-(+)-Dimethindene maleate shows lower affinities for the muscarinic M 1 (pA 2 = 6.83/6.36; pK i = 7.08), the M 3 (pA 2 = 6.92/6.96; pK i = 6.70) and the M 4 receptors (pK i = 7.00), respectively. (S)-(+)-Dimethindene maleate also is a histamine H 1 receptor antagonist ( pA 2 = 7.48).