The modelling of the relationship between QT and RR intervals is an important issue for pharmaceuticalresearch on the way to new drugs. Pharmaceutical industries have to thoroughly investigate potential effects of their medicines on QT intervals since QT prolongation is considered as a marker of the proarrhythmia risk. As QT intervals depend on RR intervals there is an obvious interest in modelling the QT-RR relationship. Static formulas to correct QT for RR are well known, but a dynamic dependencyis mainly observed.Two models of dynamic QT-RR relationships are introduced to eliminate the heart rate dependent part out of the QT interval. These models are based on heart cell measurements and simulations and are validated by Holter ECG data.