Aspirin is only an antiplatelet med. Warfarin/coumadin targets the vit K dependent clotting factors synthesized by the liver (II, VII, IX, X) it also affects the anti-clotting factors prot c and prot s. The anti-clotting factors are affected first and thus heparin overlap is often used initially until factor II is decreased. Other benefits of warfarin are oral admin, longer half-life, and it does not cause HIT (heparin induced thrombocytopenia).