In order for the mosquito to obtain a blood meal it must surmount the vertebrate physiological responses. The mosquito, as with all blood-feeding arthropods, has evolved mechanisms to effectively block the hemostasis system with their saliva which contains a complex mixture of secreted proteins. Mosquito saliva affects vascular constriction, blood clotting, platelet aggregation, inflammation, immunity, and angiogenesis. Universally, hematophagous arthropod saliva contains at least one anticlotting, one anti-platelet, and one vasodilatory substance. Mosquito saliva also contains enzymes that aid in sugar feeding and antimicrobial agents to control bacterial growth in the sugar meal. The composition of mosquito saliva is relatively simple as it usually contains fewer than 20 dominant proteins. Despite the great strides in knowledge of these molecules and their role in bloodfeeding achieved recently, scientists still cannot ascribe functions to more than half of the molecules found in arthropod saliva. One promising application is the development of anti-clotting drugs based on saliva molecules, which might be useful for approaching heart-related disease, because they are more user-friendly blood clotting inhibitors and capillary dilators.