Modified annexin proteins, including a homodimer of human annexin V, are provided. Methods for their use, such as to prevent thrombosis without increasing hemorrhage and to attenuate ischemia-reperfusion injury (IPI), are also provided. The modified annexins bind phosphatidylserine (PS) on cell surfaces, thereby preventing the assembly of the prothromkinase complex. The modified annexin decreases the binding of leukocytes and platelets during post-ischemic reperfusion, thereby restoring microvascular blood flow and decreasing organ damage.