Abstract: The cardiotonic effect of native Asclepias curassavicin L. was reported first by Prof. F. H. Lue (吕富华). A cardiac glycoside, curassavicin, was isolated from this plant collected in subtropical zone of Yunnan. Curassavicin gave positive chemical reactions of cardiac glycoside and had a digitalis-like effect on frog or mammalian hearts. When injected into lymph sac it produced a systolic arrest in frog's heart. On mammalian hearts in situ and in vitro, small doses increased the amplitude but slowed down the heart rate; toxic doses produced arrhythmia and systolic arrest. In the ECG of guinea pigs it prolonged the P-R and R-R intervals and caused an inversion of the T-wave. According to the method stated in Chinese Pharmacopeia (1953), the minimal lethal doses (± s.e.) in pigeons of curassavicin, the tinctura of this plant, digitoxin and gstrophanthin were 0.751±0.017, 549.7±19.4, 0.777±0.029 and 0.170±0.004 mg/kg respectively. Therefore curassavicin was 732 times as potent as the crude drug. The biological activity of curassavicin was higher than that of digitoxin but lower than that of g-strophanthin. The degree of accumulation in pigeons of curassavicin in 24 hours was less than that of g-strophanthin.