Increased QT /RR and Tpe /RR slopes have been shown to be independent predictors of sudden cardiac death (SCD) when analyzed over a 24-hour ECG recording. The circadian influence on the QT /RR slope is well-known but it has never been tested on the Tpe /RR slope. This work studied the inter-individual variability of the curvature and slope of QT /RR and Tpe /RR, as well as their circadian pattern in women and men. Holter ECG recordings of 385 patients with chronic heart failure (CHF) from the " MUSIC " database were analyzed. ECGs were delineated using a single-lead procedure over the first principal component lead derived to emphasize the T-wave. RR, QT and Tpe series were obtained and for each patient, a regression equation was fitted, where γ is the QT /RR or Tpe /RR curvature , and Δ is the slope of the regression pattern evaluated at the medium RR value. The median (IQR) slope was Δ QT = 0.194 (0.11), and Δ Tpe = 0.018 (0.04). The median (IQR) curvature was γ QT = 0.993 (0.17) and γ Tpe = 1.000 (0.04), respectively. The circadian pattern modulated the QT /RR and Tpe /RR curvature and slope, with statistically significant differences between day and night for QT /RR slope. No statistically significant differences in gender were found in this study. According to the results in this work, the time of the day should be considered when using QT /RR slope for SCD risk prediction, but the Tpe /RR slope is less sensitive to the circadian pattern.