In patients with heart failure (HF), low peak oxygen consumption (VO(2)) and prolonged QT interval or enhanced QT variability are associated with poor prognosis. Whether HF severity or left ventricular (LV) loading conditions can influence repolarization length is unknown. Survival, QTc interval, peak VO(2), clinical, laboratory, echocardiographic, and invasive hemodynamic data were analyzed in 154 transplant candidates; mortality was examined after a mean follow-up of 4.3 +/- 1.8 years. The relation between the QTc interval and other variables was examined using multivariate analysis and multiple correlation coefficients. Patients were stratified by peak VO(2) to study its relation with peak VO(2), mortality, loading conditions, and QTc intervals. Mean ejection fraction was 10 +/- 9%; mean cardiac index was 2.06 +/- 0.7 L/min/m(2). Seventy-one patients (47%) were dead at the end of study. Mortality and nonfatal ventricular arrythmias were higher (p <0.01) in patients with lower peak VO(2) and longer QTc intervals (p <0.001). An inverse correlation was found between QTc interval length and peak VO(2) (r = -0.790, p <0.0001). No correlation was found between QTc interval and LV loading conditions or the other analyzed variables. Thus, repolarization length measured by the QTc interval is inversely correlated with HF severity measured by peak VO(2) and is independent of LV loading conditions in patients with severe HF.