Current familial or acquired bleeding diathesis not attributable to heparin (prothrombin time greater than 15 s, a PTT greater than 36 s, fibrinogen less than 150 mg/dL); platelet count less than 50,000/gL unsupportable with platelet transfusions; creatinine greater than 2 mg/dL; severe hypertension (systolic greater than 200 mm Hg, or diastolic greater than 100 mm Hg); atrial fibrillation; known right-to-left shunts; pregnancy; breast feeding; history of anaphylactic reactions to contrast media; history or evidence of heparin-induced thrombocytopenia. Patients with underlying coagulopathy must be evaluated and cleared by Dr. Horne or a consulting NIH hematologist before they can be accepted for the treatment protocol.