The effect of positive inotropic agents on the contractile properties of myocardial muscle were studied in the cat papillary muscle preparation. For the purpose, the effects of ouabain (1 X 10<sup>-6</sup>g/ml), norepinephrine (0.05r/m1) and Aconiti tuber butanol fraction (AF(5), 1 X 10<sup>-4</sup>, 5 X 10<sup>-4</sup>, 1 X 10<sup>-3</sup>, 2 X 10<sup>-3</sup>g/ml) on the contractile dynamics of the papillary muscle preparation isolated from right ventricle of cat were observed in terms of the characteristics of isometric twitch and the lengh-tension relation, the force-velocity relation and the load-extension relation of the series elastic component of contractile model of A.V. Hill. All the studied inotropic drugs similary increased the rate and the intensity of the developed isometric tension, while shortened the time from onset of contraction to peak tension and the total duration of contraction. In the afterloaded simultaneous isotonic and isometric contraction, they also similary increased the maximal velocity of shortening accompanied with the increasing the maximum developed force. In the load-extension relation all the drugs, however, had no appreciable influence on the properties of the series elastic component. Increasing the concentration, Aconiti tuber butanol fraction produced more pronounced effect on all the studied parameters of isometric and isotonic contraction of cat papillary muscle preparation. From the aspect of contractile dynamics, it seemed that the positive inotropic effect of ouabain, norepinephrine and Aconiti tuber butanol fraction are similary achieved through an influence on the behavior of the contractile component only.