Abstract: Neferine, an alkaloid extracted from the green seed embryo of Nelumbo nucifera Gaertn, had been shown to have anti-arrhythmic action. Its effects upon the physiologic properties and the dose-effect response of isoprenaline and Ca²⁺ were studied in guinea pig atria.Neferine 30 μmol/L decreased the automaticity-inducing effect of adrenalinene in guinea pig atria. Neferine 1～100 μmol/L, in a concentration-dependent manner, inhibited the force of contraction and excitability, prolonged the functional refractory period on, the left atrium, and reduced the automaticity and contractility of the right atrium.Neferine 30 μmol/L suppressed and shifted the isoprenaline dose-effect curve to the tight non-parallelly, an action different from the action of propranolol. Neferine, as verapamil, showed dualistic action in Ca²⁺-antagonism.