We determined the antiarrhythmic effect of Rbl (from Panax notoginsengl on different ar rhythmia models and its effect on cytoplasmic Ca2+ concentrations ([Ca2+]i) in rat heart cells with fura-2 fluorescence. At doses of 30 and 50mg/Kg, Rb1 produced an antirrhythmic effect on BaClz-induced ven tricular tachyarrhythmia in rats, atria (fibrillation induced by CaCl2-ACh, and ventricular fibrillation induced by chloroform in mice. The rest [Ca22]i was 108+10.7nM in the freshly isolated rat heart cells. Sixty mM KCl caused an increase in [Ca2+]i to 379.4±77nM. Rb1 from 0.1 to 0.8mM significantly reduced this increase in a concentration-dependent manner, mM Rb1 (0.4mM) also completely inhibited the increase in [Ca2+]i induced by 1 μM isoprenaline. The radioligand binding study in rat heart cells showed that Rb1 did not change the Bmax. and Kd values of [3H]-dihydroalprenolol binding. These data suggest Rb1 can inhibit Ca2+ entry through voltage-dependent and receptor-linked Ca2+ channels, and that this is related to its antiarrhythmic effect, Drug Dev. Res. 39: 179-183.