In the anaesthetized cat, SCOA ( Miroton ), a product which contains extracts from Scilla , Convallaria , Oleander and Adonis , displays not only its well-known positive inotropic effect but has also constrictor effects on veins when applied in intravenous doses of 21.5-100 GPU /kg ( GPU = guinea-pig units, i.e. cardiotoxic equivalents related to 1 g body weight of guinea-pigs). The latter effect differs in that it is somewhat more prolonged. With intraduodenal administration the doses required to achieve equal peak effects as with intravenous injection are about 4 times larger and this suggests a relatively good enteral availability in the cat. SCOA constricts not only veins but also arteries. However, this latter effect is comparatively small and occurs only after intraarterial infusion of high doses (9.1 and 91 GPU /min, respectively).--The cardiac glycosides contained in the drug product primarily account for its vasoactive qualities. The venous constrictor effect correlates with the guinea-pig units. In qualitative respects, the pure glycosides cymarin , convallatoxin , proscillaridin , and scillaren exert equal effects. There is, however, evidence that the correlation between the effect on veins and on the heart differs for the glycosides tested. Based on equal guinea-pig units, the adonis extract, for instance, acts on capacitance vessels about twice as much as scilla , oleander and convallaria extracts. Cymarin , too, has a stronger effect on veins than would be expected from its cardiotoxic effect. The action on arteries and veins are based on different mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)