The present experiment was desinged to investigate the effects of Tongdosan water extracts on the Cardiovascular System in the Experimental Animals. Thus, the changes of blood pressure and heart rate were measured after oral admini- stration. Measurment of Mortality rate was observed for measuring the effect of Tongdosan water extract. Tongdosan water extract against pulmonary thrombo- embolism induced by collagen the mixture(0.1ml/10g, 2mg/kg B.W) plus serotonin(5mg/kg B.W) in mouse. The effect of Tongdosan water extract was examined by observing the change of collagen-induced platelet aggregation, coagulation activity, ex vivo and in vitro fibrinolytic activity of euglobulin fraction in rats. The results were summarized as followings. 1. Tongdosan dropped the blood pressure in spontaneous hypertensive rat. 2. The drug increased the auricular blood flow in rabbit. 3. The drug relaxed the artery contraction by pretreated norepinephrine in rat. 4. The drug inhibited the death rate of mouse which was led to thromboembo- lism by serotonin and collagen. 5. The drug inhibited the platelet aggregation in rat. 6. The drug prolonged the prothrombin time and activated partial thromboplastin time on the test of plasma coagulation factor activity in rat, but was not valuable. 7. The drug reduced the fibrinogen lyses time of rat ex vivo assay and lyses area was increased. 8. Tongdosan reduced fibrinogen lyses time of rat in vitro assay. According to the above mentioned results, Tongdosan increased the blood flow and dropped the blood pressure by the dilation of blood vessel. And the drug presented the antithrombin acivity, inhibited the platelet aggregation.