Only recently the QT interval (QT) variability has been successfully exploited in rats for cardiac control assessment and it has been demonstrated that QT variability markers have a similar physiological meaning in humans and rats. However, some studies suggest that the dependence of QT on the previous RR interval (RR) might differ between humans and rats. Thus, the aim of this study was to compare the QT-RR relation in humans and rats. Electrocardiogram (ECG) was recorded for 10 minutes in supine position (REST) and during sympathetic activation induced by head up tilt test at 90° (T90) in 23 young healthy subjects (11 males, age 26.3±5.6 years). ECG was also telemetrically recorded in 9 Wistar (WI) and 14 wild-type Groningen (WT) rats during the dark period for one hour. The two rat strains are known to exhibit different social traits that are mirrored by a diverse sympathetic control. RR and QT beat-to-beat series were computed. Pearson correlation coefficient r between RR and QT was calculated for each subject, or animal, within each experimental condition. We found that r was positive in humans and decreased from REST to T90 (0.48±0.18 vs 0.34±0.25), while r was negative in rats and did not differ between WI and WT (-0.32±0.17 vs -0.26±0.18). r absolute value was significantly higher in humans than in rats (0.41±0.22 vs 0.27±0.18), when data were pooled together regardless of the experimental condition or rat strain, respectively. Our results showed that relation between QT and RR is of opposite sign in humans and rats and that the strength of the QT-RR association is lower in rats than in humans. We conclude that attention should be paid in the use of the rat model in translational studies assessing the QT-RR relation given that it can be different in humans and rats.