In chronic heart failure, very-low-frequency (VLF) oscillations (0.01-0.04 Hz) in heart rate and blood pressure may be related to periodic breathing, although the mechanism has not been fully characterized. Groups of ten patients with chronic heart failure and ten healthy controls performed voluntary periodic breathing with computer guidance, while ventilation, oxygen saturation, non-invasive blood pressure and RR interval were measured. In air, voluntary periodic breathing induced periodic desaturation and prominent VLF oscillations when compared with free breathing in both patients [RR interval spectral power from 179 to 358 ms2 (P<0.05); systolic blood pressure (SBP) spectral power from 3.44 to 6.25 mmHg2 (P<0.05)] and controls [RR spectral power from 1040 to 2307 ms2 (P<0.05); SBP spectral power from 3.40 to 9.38 mmHg2 (P<0.05)]. The peak in RR interval occurred 16-26 s before that in SBP, an anti-baroreflex pattern. When the patients followed an identical breathing pattern in hyperoxic conditions to prevent desaturation, the VLF RR interval spectral power was 50% lower (179.0+/-51.7 ms2; P<0.01) and the VLF SBP spectral power was 44% lower (3.51+/-0.77 mmHg(2); P<0.01); similar effects were seen in controls (VLF RR power 20% lower, at 1847+/-899 ms2, P<0.05; VLF SBP power 61% lower, at 3.68+/-0.92 mmHg2, P=0.01). Low- and high-frequency spectral powers were not significantly affected. Thus periodic breathing causes oxygen-sensitive (and by implication chemoreflex-related) anti-baroreflex VLF oscillations in RR interval and blood pressure in both patients with chronic heart failure and normal controls.