The model was established in male rabbits with experimental atherosclerosis, which was induced by diet cholesterol (0.5 g per day for 8 weeks), by means of intravenous injection of one unit of pituitrin (P.P.). To evaluate the effects of aspirin, heparin and viper venom (VV) on this model, 26 male rabbits were divided randomly into four groups: group A (GA) as control, group B (GB) treated with heparin (10mg, i.v.), group C (GC) with VV (0.08 arginine esterase activity units), group D (GD) with both heparin and VV. Aspirin (30 mg) was given orally before experiment. The results showed that the rate of coronary thrombosis was 11.26% in GA, 8.10% in GB, 9.17% in GC, and 7.56% in GD respectively. The difference between each of three treated groups and the control one was significant (P < 0.005, 0.05, 0.001, respectively). Such a difference can also be found between GA and that without oral aspirin (11.26% vs 16.39%, P < 0.001). The beneficial effects of heparin and VV may be due to their inhibitory effects on different steps of thrombosis, i.e., heparin can prolong the coagulation time, and VV can inhibit platelet aggregation and decrease the concentration of plasma fibrinogen. It is concluded that heparin, viper venom, and especially their combination would be useful in the treatment of human acute coronary syndromes.