The purpose of this study is to see if a naturally-occurring hormone called erythropoietin changes the action of platelets in the blood. Patients with heart attacks are treated with medicines to reduce the clotting action of platelets. This study is trying to determine whether erythropoietin alters the clotting action of platelets in patients receiving anti-platelet medicines. It is important to understand the effects of erythropoietin on platelets since preliminary studies in animals suggest that erythropoietin may protect the heart from damage during a heart attack.