“…Attempts have been made to relate the changes in the ECG to quinidine blood concentration, but have been limited by the use of nonspecific assays for quinidine and abbreviated descriptions of the time course of drug action (Cheng, Sutton, Swisher & Sutton, 1956;Heissenbuttel & Bigger, 1970;Josephson, Seides, Batsford, Weisfogel, Caracta, Lau & Damato, 1974;Cho, 1973;Edwards, Hancock & Sayner, 1974). The development of improved methods for measuring the ECG and specific assays for quinidine (Guentert, Coates, Upton, Combs & Riegelman, 1979) has allowed us to define quantitative relationships between quinidine concentrations and ECG changes in man and to extend the qualitative description of these changes.…”