The following practises and directors participated in the study (the sites are listed in decreasing order of number of patients enrolled): Lutheran General Hospital, Niles, Illinois—W. Fried, M. Pubentz; Physicians, Inc., Lima, Ohio—D. Parker; Idaho Cardiology Associates, Boise, Idaho—F. Badke; North Clinic, Robbinsdale, Minnesota—V. Krug; Rockwood Clinic P.S., Main, Spokane, Washington—J. S. Pennock; Wenatchee Valley Clinic, Wenatchee, Washington—R. Kirby Primm, L. Vaughn; Framingham Heart Center, Framingham, Massachusetts—J. Dangel, S. R. Hewett; Clinic Pharmacy Consultants-Brainerd Medical Center, Brainerd, Minnesota—B. Twamley, R. Sorenson; Woodland Healthcare, Woodland, California—L. Smith, T. Fajerson; Cardiology, PC, Syracuse, New York—S. O’Donnell; Health Care American Corp, Bradenton, Florida—C. Hoffman; DuPage Medical Group, Department of Cardiology, Winfield, Illinois—N. Kinsley; Camino Medical Group, Sunnyvale, California—S. Edwards; Ohio Valley Heartcare, Evansville, Indiana—L. Janeira, J. Robb; Desert Medical Group/Oasis IPA, Palm Springs, California—H. F. Bellaci, J. Bellaci; Anchor Health Center, Naples, Florida—M. Means; Sutter Gould Medical Foundation, Modesto, California—J. E. Baker; Hannibal Clinic Inc., Hannibal, Missouri—L. Chalton; Saratoga Cardiology, Saratoga Springs, New York—R. Sheldon, D. Kandath; Lima Memorial Hospital, Lima, Ohio—C. L. Thompson, J. Recker; Staten Island University Hospital, Staten Island, New York—M. Howard; Jacksonville Cardiovascular Clinic, Jacksonville, Florida—R. A. Benson; River Valley Healthcare, Silvis, Illinois—K. Carroll; Family Physician Incorporated, N. Canton, Ohio—H. Marshall; Internal Medicine of Northern Michigan, Petoskey, Michigan—P. D. Blanchard; Redmond Internal Medicine, Redmond Oregon—D. Palmer, C. Gangan; Grove Hill Medical Center, New Britain, Connecticut—M. S. Werner; Olean Medical Group, Olean, New York—H. D. Storch, T. L. Buzzard; Internal Medicine Associates of Greenville, Greenville, South Carolina—J. S. Moore; Magan Medical Clinic, Covina, California—R. Sakamoto; Owatonna Clinic—Mayo Health System, Owatonna, Minnesota—T. Price; Dearborn Cardiology, Dearborn, Michigan—S. Dabbous; Westchester Medical Group, White Plains, New York—B. Newman; Central Cardiology Medical Clinic, Bakersfield, California—W. Nyitray; Salem Clinic, Salem, Oregon—M. Smith; East Carolina University, Greenville, North Carolina—C. Estrada; Northwest Primary Care Group, Milwaukie, Oregon—D. McAnulty, P. Devisser; The William W Backus Hospital, Norwich, Connecticut—S. Johnson; Jefferson City Medical Group, Jefferson City, Missouri—C. Balcer; Saint Louis University Department of Neurology, St Louis, Missouri—S. Cruz-Flores, E. Holzemer; Wellspan Health, Yorktowne, York, Pennsylvania—J. D. Horton; Mercy Medical Center, Canton, Ohio—M. Cudnik; Cardiovascular Group, Lawrenceville, Georgia—B. Craig-Allen; Asheville Cardiology Assoc, Asheville, North Carolina—W. Wharton, A. Moser; Cardiac Consultants Chartered, Bethesda, Maryland—L. Chappell; Valley Care Health System, Pleasanton, California—N. Huynh; Bloomington Hospital, Bloomington, Indiana—K. Kalotta; Samaritan Anticoagulation Service, Corvallis, Oregon—R. Stockberger; Covenant Clinic, Waterloo, Iowa—D. Kohls; Dartmouth-Hitchcock Nashua, Nashua, New Hampshire—L. Cook; Cardiology Consultants, PC, Hamden, Connecticut—A. M. Radoff; Seventh Avenue Family Health Center, Fort Lauderdale, Florida—J. Berges; Diagnostic Cardiology, P.A., Jacksonville, Florida—P. D. Kuhlman; Norlanco Medical Associates, Elizabethtown, Pennsylvania—J. Rittenhouse; University of Texas Medical Branch, Galveston, Texas—H. von Marensdorff; Bend Memorial Clinic, Bend, Oregon—M. Hegewald; Memorial Primary Care Center, Hollywood, Florida—J. Beck; Batey Cardiovascular Center, Bradenton, Florida—D. Calabrila, E. J. Sanchez; Western Montana Clinic, Missoula, Montana—W. B. Bekemeyer, D. Ramsey; Winona Clinic, Winona, Minnesota—L. Tschumper; Cardiac Consultants, Lancaster, Pennsylvania—M. Lesko; Hattiesburg Clinic, Hattiesburg, Mississippi—A. J. Jackson; Bryn Mawr Medical Specialist Association, Bryn Mawr, Pennsylvania—H. Mayer; River Valley Healthcare, Moline, Illinois—B. Cady; Cardiovascular Group, Snellville, Georgia—L. Lesser; Medicor, Bridgewater, New Jersey—P. Saulino, C. Hartpence; Bond Clinic, P.A., Winter Haven, Florida—P. Lundsford. K. Bhatia; University of Cincinnati-Pharmacy Anticoagulation Services, Cincinnati, Ohio—J. McQueen; Senior Healthcare Center, Gainesville, Florida—M. L. Breeser; North Canton Medical Foundation, North Canton, Ohio—H. M. Schenker; Manor Family Health Center, Millersville, Pennsylvania—J. Ichter; Cardiology Associates of Central Florida, Ocala, Florida—L. McDaniel; Cardiovascular Associates Ltd, Chesapeake, Virgina—S. R. Jones; Woodburn Medical Clinic, Woodburn, Oregon—F. Golden; Rockwood Clinic North, Spokane, Washington—C. Laudenbach, J. S. Pennock; Wachspress, Shatkin & Rainear, Vineland, New Jersey—L. Assink; Chambersburg Hospital, Chambersburg, Pennsylvania—D. Grant; Wellspan Pharmacy-Dallastown, Dallastown, Pennsylvania—T. G. Williams; Pulmonary & Critical Care Associates, Ypsilanti, Michigan—W. F. Patton; Island Cardiac Specialist, Mineola, New York—P. Ragno; Portland Cardiovascular Institute 2, Portland, Oregon—R. Chelfky; River Valley Healthcare ACS, Bettendorf, Iowa—W. Langley; Consultants in Cardiology, Farmington Hills, Michigan—G. M. McKendrick; Portland Cardiovascular Institute 1, Portland, Oregon—R. Chelfky; Cleveland Clinic Florida, Weston, Florida—B. Fernandez; BiState Medical Consultants, St Louis, Missouri—P. M. Stein, C. B. Lomnel; Medical Consultants, PC, Muncie, Indiana—J. Bow; Cardiovascular Associates of South Florida, Coral Gables, Florida—J. S. Palmer; Parkway Cardiology Associates, Oak Ridge, Tennessee—S. Cooke; Northwest Georgia Diagnostic Clinic, Gainesville, Georgia—J. Jackson; Cardiovascular Associates, Kingsport, Tennessee—L. H. Cox; Heart Place, Dallas, Texas—C. N. Bowers; Rockwood Clinic, Spokane, Washington—C. Laudenbach; J. S. Pennock; Delaware Heart Group, Newark, Delaware—C. Bowens; Abilene Diagnostic Clinic, Abilene, Texas—P. Howard.