1. From the Center for Platelet Function Studies, Department of Pediatrics (A.L.F., M.D.L., M.L.F., M.R.B., A.D.M.), Division of Cardiovascular Medicine, Department of Medicine (M.I.F., Y.L.), University of Massachusetts Medical School and the Cardiac Catheterization Laboratories (M.I.F.), UMass Memorial Health Care, Worcester, Mass.