Abstract: A substance (total cardiac glycosides) was obtained from Calotropis gigantea L. Dryander (Asclepidaceae) by the Institute of Botany of Kunming, Academia Sinica. The authors reported on the cardiotonic action and biological potency of the substance as follows: 1. By experiments on hearts (frogs, cats and rabbits) in situ and Langendorff's method in perfused isolated heart (guinea-pigs, cats), it was found that the substance was cardiotonic. 2. The changes in EKG on rabbits receiving intravenous injections of the substance were similar to other cardiac glycosides. 3. When assayed according to the method for digitalis of Chinese Pharmacopeia, the pigeon unit of the substance was found to be 2.82 mg/kg.