Aims We undertook this study to evaluate potential changes in cerebral vasoreactivity in patients with cardiac failure and their consequent dependence upon cardiac functional variables. Methods and Results A total of 50 patients with various degrees of heart failure, 20 age-matched controls and 20 normal controls were examined. Cerebrovascular reactivity was examined with the carbon dioxide technique. Mean flow velocities of both middle cerebral arteries as well as end-tidal carbon dioxide partial pressure were continuously registered. Normal controls were examined on two different occasions, to evaluate the technique's reproducibility. Cerebrovascular reactivity was significantly reduced in all examined patients as compared to controls, and in NYHA IV as compared to NYHA II and III patients. A significant relationship between cerebrovascular reactivity and left ventricular ejection fraction was evident. Reproducibility of the technique was satisfactory. Conclusion Our study provided evidence of significantly reduced cerebrovascular reactivity in patients with cardiac failure, which was significantly related to the NYHA grade and the left ventricular ejection fraction.