Abstract: AimTo investigate the mechanism of the positive inotropic effect of oxyphenamone． MethodsWith the patch clamp technique and whole cell recording, the sodium and L type calcium currents of myocytes isolated from ventricular myocardium of adult guinea pigs were studied． Results5-50 μmol·L^-1oxyphenamone not only significantly inhibited Na+ current， but also promoted the process of inactivation and prolonged the recovery time of the inactivation． The action of oxyphenamone on L type calcium channel was dual． The inward calcium current was increased with 2-10 μmol·L^-1oxyphenamone but decreased when the concentration of the drug was elevated to 20-50 μmol·L^-1 ． ConclusionThe mechanism of the positive inotropic effect of oxyphenamone is neither due to the activation of sodium channel nor entirely depending upon the activation of L type calcium channel． The effects of inhibiting sodium current and， at a high concentration， blocking L type calcium current suggest that oxyphenamone may have an antiarrhythemia action．