The aim of this study was to test the hypothesis that the increased ventilation to carbon dioxide production relationship on exercise associated with chronic cardiac failure may be due in part to changes in respiratory pattern, causing an increase in anatomical dead space ventilation. In order to assess the effect of changes in respiratory pattern on the relationship between ventilation and carbon dioxide production, normal subjects exercised at the same level at three different respiratory rates (normal, 25% slower, 25% faster). Nine healthy subjects were recruited from amongst hospital staff volunteers. Minute ventilation, carbon dioxide production and oxygen consumption were measured. There were no significant changes in ventilation, carbon dioxide production, or the correlation between ventilation and carbon dioxide production. This finding lends support to the view that changes in respiratory pattern can only be responsible for a very small proportion of the VE/VCO2 slope difference between chronic cardiac failure and normals.