Lampranthus spectabilis is an ornamental plant which belongs to one of the Aizoaceae family as an one-year herb. There are no illustrations on the references that Lampranthus spectabilis has been made use for the purpose of the medicinal plant among the traditional herb doctors and the laymen. However, it has the specific characteristics to be analogous to the Cactaceae family in the botanical classification. Besides, mescaline, the main ingredient of Peyote cactus, demonstrates the sympathomimetic effect as well as the psychotomimetic effect. The authors called our attention to the resemblance to the botanical family between Aisoaceae and Cactaceae, and made a survey whether the alcohol extract of Lampranthus spectabilis might possess any pharmacological effect on the isolated heart of clam or not. The results of the experiment were as follows. 1. Administration of LX to the isolated heart of clam produced an inhibitory effect on the cardiac motility in proportion to its concentration 10^-4, 5 X 10^-4 and 10^-3 g/ml respectively. 2. Administration of LX 5 X 10^-4 and 10^-3 g/ml produced the blockade effect on the cardiac motility pretreated with serotonin 10^-7 and 10^-4 g/ml, as well as with methysergide 10^-6 and 10^-5 g/ml. 3. Administration of LX 5 X 10^-4 g/ml produced no effect on the cardiac motility pretreated with acetylcholine 10^-7 g/ml. 4. Administration of LX 5 X 10^-4 g/ml produced the blockade effect on the cardiac motility pretreated with barium chloride 10^-4 g/ml, as well as with prostaglandin 20μg. Consequently, it is concluded that the alcohol extract of Lampranthus spectabilis has an effect of depression on the motility of the isolated heart of clam. Its mechanism of action might be due to a direct action on the heart. the heart.