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