The aim of the study: Comparison between breathing on the 0.1 Hz and 0.33 Hz. At a breathing frequency of 0.10 Hz, differences in baroreflex sensitivity (P<0.01) became evident, even though these differences were not apparent at the 0.33-Hz breathing frequency. CONCLUSIONS: The frequency of 0.10 Hz represents a useful and potentially important one for controlled breathing, at which differences in blood pressure-RR interactions become evident. These measurements of short-term circulatory control might help in risk stratification for sudden cardiac death.