A 17.beta.-unsaturated aldehyde analogue [3.beta.,14.beta.-dihydroxy-5.beta.-pregn-17.beta.-trans-20-en-22-al (7)] of the cardenolides was synthesize and studied. In earlier studies, unsaturated aldehydes were highly active electrophiles, more active, for example, than unsaturated nitriles or methyl esters. The synthesis followed in part a scheme previously reported by Thomas for the syntheses of the 17.beta.-unsaturated nitrile 9 and the 17.beta.-unsaturated methyl and ethyl esters 8 and 10. Both 9 and 8 are more Na+,K+-ATPase inhibiting and slightly less inotropic than digitoxigenin (1b). The unsaturated aldehyde 7 was less Na+,K+-ATPase inhibiting (I50 [50% inhibition] = 9.9 .+-. 0.7 .times. 10-7 M) and less inotropic (100% increase in contractile force at 8.5 .+-. 1.0 .times. 10-6 M) than 1b (I50 = 4.6 .+-. 1.6 .times. 10-7 M; 100% increase at 3.0 .+-. 1.0 .times. 10-7 M).