17-(2-Piperidylmethyl) − 3β, 17β-androstane diol lactate (Ro 2-7302/4) has an activity equal to that of quinidine in diminishing maximum rate of the electrically driven isolated rabbit auricle. It is approximately 16 times as active as quinidine in antagonizing acetylcholine-induced auricular fibrillation in the dog. It is slightly more active than quinidine in antagonizing aconitine-induced tachycardia in the same species. The safety margin of this drug, as measured by the ratio between minimal anti-fibrillatory doses and those producing marked blood pressure and ECG changes, is greater than that of quinidine.