Objective To study the effect of different doses of monocrotaline in combination with isopropylarterenol on the hemodynamic resonse, heart index and right heart hypertrophy index in rats.Methods Sixty-four healthy adult SD rats, male:female=1∶1, body weight 200-250 g, were randomly divided into blank control group (n=16) and three model groups (n=16 in each group).The high dose model group (n=16) received i.p.injection of monocrotaline 80 mg/kg once and epinephrine 10 mg/kg once daily for one week.The moderate dose group received i.p. injection of monocrotaline 55 mg/kg once and epinephrine 8 mg/kg once daily for one week.The low dose group received i. p.injection of monocrotaline 30 mg/kg once and epinephrine 3 mg/kg once daily for one week.The rats were fed for 6 weeks, and then pulmonary artery pressure and right ventricular pressure were tested and heart index and right ventricular hypertrophy index were determined.Results Compared with the control group, the mean pulmonary artery pressure and right ventricular systolic blood pressure in the low dose monocrotaline group were not significantly changed, but significantly changed in the moderate dose monocrotaline group ( P<0.05) .The heart index and right ventricular hypertrophy index in the low dose monocrotaline group were not significantly changed, but in the moderate dose monocrotaline group, the heart index was significantly reduced ( P<0.01 ) and the right ventricular hypertrophy index was significantly increased ( P<0.05 ) .Conclusions The use of a single injection of 55 mg/kg monocrotaline in combination with continuous injection of 8 mg/kg isopropylarterenol once daily for one week can ensure the survival rate of rats, and the successful formation of pulmonary artery hypertension, leading to heart weakness.