To evaluate the effect of an acute reduction in VV on QTd, 14 men with heart falure (HF) (74.5 ± 2 years) and 11 healthy controls (68 ± 2 years) were studied. Fifteen minutes of -15 and -40 mm Hg of lower body negative pressure (15 LBNP and 40 LBNP, respectively) was applied to reduce venous return. At baseline and during LBNP, QTd was measured with an 87-lead body surface mapping device, chamber volumes were assessed by radioisotope ventriculography, blood pressure (BP) and heart rate (HR) were continuously monitored, and blood samples were obtained for norepinephrine (NOR) levels. 15 LNBP induced a significant decrease in VV, but did not change BP and HR in both groups; NOR levels increased significantly (p<0,05) in the control group (from (286.7 ± 31.5 to 388.8 ± 41.2 pg/ml) and in HF patients (from 405.8 ± 56 to 477.6 ± 47 pg/ml); QTd significantly (p<0,05) decreased in the Control group (57.2 ±3.8 vs. 49.1 ±3.4 ms) and in HF patients (67.8 ±6 vs. 63.7 ±5.9 ms). No further decrease in VV or QTd was produced by 40 LNBP, but it did increase NOR levels in both groups reaching, respectively, 475.5 ±34 and 586.5 ± 60 pg/ml (p<0,05) in the control group and HF; BP did not change, but HR increased in both groups. Conclusion: An acute LBNP-induced reduction in VV caused a decrease in the QTd of elderly men irrespective of the existence of HF. As increased sympathetic activity with more intense LBNP was not accompanied by further changes in QTd, altered QTd may be better related to changes in VV than to autonomic nervous system activity.