Abstract: The extract of Folia Thevetia Peruviana Merr.,or Thevetia Neriifolia(Jussieu)was inves- tigated with regard to its actions on the heart.The galenical preparation(tincture)of the leaves was studied and was found to exhibit a digitalis-like action on the cat heart.In small doses it showed a stimulant action,but in large doses the ventricular contraction depressed and stopped.A small dose of 0.03 gm/kg,injected by vein,raised the blood pressure,while large doses of 0.15 gm/kg caused the blood pressure to drop rapidly.When assayed according to the Chinese Pharmacopeia(1953),the cat unit of the extract was found to be 0.205 gm.per kg. The toxicity of the leaves of this plant was similar to that of digitalis.Nausea,vomiting,cardiac disorder etc.were the chief toxic actions.Like thevetin,the galenical preparation of the leaves of Thevetia Peruviana showed more prompt action but less chance of cumulation than digitalis. These facts may serve as guides to its further investigation.