In this paper, the heart is treated as a dynamical system.The fact hat the heart is a dynamical system in the mathematical sense of the word has been exemplified by the Erlang distribution of the RR interval, a phenomenon symptomatic of the Poincaré return time in mixing systems.More specifically, here, we look at the issue of the QT prolongation from a dynamical system theory point of view.The fact that the QT is somehow "modulated" by the RR has led to such conceots as the corrected OT interval.Here, the same problem is approached from the point of view of how the RR dynamics and the QT dynamics are intertwined.