The relationship between the inotropic effect and chemical structure of 15-crown-5 and 18-crown-6 derivatives was studied in experiments in open-chest anaesthesized cats, by using computer-aided analysis. The findings showed that the 15-crown-5 derivatives produced more pronounced cardiotropic effect and they were less toxic than 18-crown-6 derivatives. Computer-aided analysis revealed pharmacophoric groups which are responsible for cardiotropic (negative inotropic) activity in the series of crown ether derivatives.