1. Department of Nuclear Medicine Service, Veterans Affairs Hospital
2. Rhythmometry Laboratory, College of Biological Sciences, University of Minnesota, St. Paul, Minnesota
3. Department of Pathology & Laboratory, Veterans Affairs Hospital
4. R&D Systems, Inc., Minneapolis, Minnesota
5. Laboratory Medicine, Swedish Covenant Hospital, Chicago, Illinois
6. Cardiology Group, MacNeal Hospital, Berwyn, Illinois
7. Department of Cardiology, Veterans Affairs Hospital
8. Veterans Affairs Hospital, Little Rock, Arkansas, U.S.A