Unfractionated heparin (UFH) and low molecular weight heparins have been used as anticoagulation agents in cardiovascular clinics for decades. However, these molecules also have potent antiangiogenic effects. Whereas, angiogenesis may be the most crucial determinant of the prognosis of cardiovascular diseases, and except some special situation, antiangiogenic effect is not desirable in the most of the cardiovascular disease. In this study, we aimed to compare the antiangiogenic potency of UFH, enoxaparin, and tinzaparin. The antiangiogenic efficacies of UFH, enoxaparin, and tinzaparin were examined in vivo by using the chick chorioallantoic membrane (CAM) model. Twenty fertilized eggs were used for each studied drug. Drug solutions were prepared in 10 and 1 IU/10 mu l concentrations. Decreases in the density of the capillaries were assessed and scored. All three drugs showed antiangiogenic effects on the chick CAM at the 10 IU/10 mu l concentration. However, the antiangiogenic score of the UFH was significantly higher than that of enoxaparin and tinzaparin at 1 and 10 IU/10 mu l concentrations. UFH had stronger and antiangiogenic potential than enoxaparin and tinzaparin. However, tinzaparin showed dose-dependent antiangiogenic effects. We think that an anticoagulant molecule with a less and dose-dependent antiangiogenic effect, as in the case of tinzaparin, may be more desirable in case of cardiovascular disease related with insufficient angiogenesis. Blood Coagul Fibrinolysis 23: 218-221 (C) 2012 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.