In our study, we demonstrated that DV-7028: (3-[2-[4-(4-fluorobenzoyl)piperidin-1-yl]ethyl]-6, 7,8,9-tetrahydro-2H-pyrido [1,2,-a]-1,3,5-triazine-2, 4(3H)-dione maleate)--a selective 5-HT2A receptor antagonist, inhibited thrombus formation in the arterial thrombosis model and was completely ineffective in the prevention of venous thrombosis in the rat. In washed platelets prelabelled with 3H-serotonin, DV-7028 inhibited, in a dose-dependent manner, the collagen-induced secretion of serotonin. However, the uptake of serotonin into platelets was not affected by this substance. Administration of DV-7028 also inhibited platelet aggregation in the whole blood and platelet-rich plasma (PRP) induced by collagen, and diminished serotonin-induced aggregation of rat platelets in the presence of a sensitizing but nonaggregating amount of ADP, whereas it did not modify aggregation in PRP when induced by ADP. DV-7028 caused a concentration-dependent, almost parallel shift to the right of the concentration-response to serotonin for its pressor effect in the rat perfused tail artery. The present data demonstrate that DV-7028 exhibits 5-HT2A receptor antagonistic properties in the rat cardiovascular system, exhibits antithrombotic effect in the model of arterial but not venous thrombosis in rats. These results constitute further evidence of the possible importance of serotonin as a mediator of platelet thrombosis in arteries. Moreover, they can provide a useful tool for the prevention of various thrombotic diseases.