Background Heart failure is associated with an increased risk of ventricular arrhythmias. Increased QT variability has been proposed as a marker of arrhythmia risk (1). We examined QT variability in a model of heart failure. Method To induce heart failure, adult male ferrets underwent ascending aortic banding (n=5) or sham operation (n=3). Operations were performed with isoflurane 2-3% inhaled anaesthesia and meloxicam analgesia (0.2mg/kg IM). Post-operatively, intermittent telemetric ECG recording was performed at baseline and end stage heart failure. These were analysed to obtain mean RR and QT interval, from which QT Variation Index was calculated as a normalised ratio of QT to RR variance. Mean beat-to-beat variation in RR and QT intervals were measured, from which Short Term QT Variation Index was calculated as a log ratio of QT to RR beat-to-beat variation. Statistical analysis was performed using Student’s T-Test. Results (see summary table) Mean QT interval increased from experiment start to finish only in the heart failure group. No significant change in beat-to-beat variation of RR or QT interval was observed in the heart failure group as a whole. A subgroup within the heart failure group was identified in which beat-to-beat RR variation declined from baseline to end-stage heart failure (n=3, mean change -39.9% SD 13.4, p<0.05) and this was associated with increased beat-to-beat QT variation (mean change +57.8% SD 30.7 p<0.05). This increase was not observed in heart failure subjects without reduced beat-to-beat RR variation (mean change -16% SD 36, ns) or in control subjects (mean change +14.7% SD 23.3, ns). Conclusion In this model induction of heart failure causes QT prolongation but not increased QT temporal dispersal. However, a heart failure subgroup is noted in which reduced beat-to-beat RR variability is associated with increased beat-to-beat QT variability. The finding of a distinct group with increased temporal heterogeneity of repolarisation is in keeping with findings from other models (2) and warrants further investigation.