It is usually postulated that the side chain attached to 17β position on the steroid nucleus of the cardioactive glycosides is a major determinant of their pharmacological activity. A new aminosteroid (LND 623) has been prepared. Despite the fact that the structural features quoted above are lacking, the product demonstrates a strong inotropic effect. LND 623 was active at the same range of concentrations as ouabain or digoxin. However, the maximum increase of the contractile force was significantly higher. The strength of the inotropic action is not modified in the presence of propranolol. The preliminary results suggest that the molecular requirements for the interaction of the drugs with the ‘inotropic receptor’ may be re-examined.