On measuring the percentage of QTc interval prolongation, the pharmacokinetic and pharmacodynamic profiles of i.v. matrine or oxymatrine in rabbits were analyzed by combined pharmacokinetic and pharmacodynamic model. The plasma concentration--time profiles of the two drugs can be described by a two--compartment open model, and the relationship between effect and effect compartment concentration of both drugs can be represented by the sigmoid Emax model. Marked differences in pharmacokinetic and pharmacodynamic parameters between the two drugs were found, but their pharmacokinetic and pharmacodynamic properties were dose--independent in the dose ranges used in the experiment.