Background: A circadian and seasonal variation of QT dispersion (QTd) has been shown in healthy individuals. Nevertheless, no data exist regarding the weekly influences on the QTd in healthy individuals and in patients with coronary heart disease (CHD). Design: This study was designed to determine whether there is a weekly variability of QTd in healthy individuals and in patients with CHD. Methods: In this prospective registry study, 53 patients with documented CHD and 57 healthy control subjects were involved. Resting electrocardiograms (ECGs) with double amplitude were recorded at a speed of 50 mm/s on Monday and Friday mornings. QT intervals were measured and QTd were determined by calculating the difference between maximum and minimum QT intervals. Then, rate-corrected QTd (QTcd) were calculated using Bazett’s formula. Results: There was a significant weekly variation of QTd in control subjects (39.3 ± 6.3 vs. 36.2 ±6.1 ms) (p < 0.05) and in patients (56 ± 7.3 vs. 47.4 ± 5.4 ms) (p < 0.0001). There was also a significant weekly variation of QTcd both in control subjects (33 ± 5.3 vs. 30.7 ± 5.6 ms) (p < 0.05) and in patients (47.4 ± 6.4 vs. 41.9 ± 5.4 ms) (p < 0.0001). Conclusions: There is a weekly variation of QTd and QTcd in healthy individuals and in patients with CHD, both with a Monday preference. This fact should be taken into consideration during the chronopharmacological treatment or advisal of primary or secondary preventive measures to these subjects or patients.