Repolarization duration is highly dependent on heart rate. A major concern when evaluating dispersion of repolarization is the possible influence of heart rate on the magnitude of dispersion. Another consideration relates to a potential relationship between overall duration of repolarization and the magnitude of dispersion, that is, whether patients with longer repolarization duration present with increased or decreased dispersion of repolarization. Therefore, the following relationships were studied in 380 normal subjects, 68 coronary artery disease (CAD) patients, and 41 long QT syndrome (LQTS) patients: the magnitude of dispersion (JTd) versus cycle length (R-R) and dispersion versus repolarization duration (QTc interval). Dispersion of repolarization (JTd), measured as the maximal difference in JT interval duration between precordial leads, was significantly higher in LQTS patients than in normal subjects or CAD patients (120 +/- 72 vs 53 +/- 42 and 48 +/- 22 ms, respectively). In neither normal subjects, CAD patients, or LQTS patients were there significant relationships between the magnitude of dispersion and the R-R interval (r = .094, .158, and .233, respectively; not significant) and between the magnitude of dispersion and QTc duration (r = .0443, -.094, and .126, respectively; not significant). In normal subjects, CAD patients, and LQTS patients, the magnitude of dispersion is not significantly related to heart rate, indicating that there is no need for heart rate adjustment of dispersion parameters. In addition, there is no significant association between the magnitude of dispersion and duration of repolarization.