The authors carried out rheoencephalographic, electrocardiographic, electroencephalographic, laboratory and radiological investigations in 30 patients with valvular heart diseases in different stages of circulatory failure. In the analysis of EEG and REG tracings the degree of changes, their character and location were taken into account. The analysis of REG tracings included evaluation of their symmetry, amplitude, area of waves and synchronism of changes in the record. On the basis of these results and correlations found between them the authors have reached the following conclusions: 1. The morphological features of REG tracings depend on the character of arrhythmia, value of arterial blood pressure and efficiency of venous circulation. 2. In 26 patients REG investigations demonstrated presence of generalized changes varying in intensity. 3. In 8 patients focal changes were present. 4. With increasing intensity of circulatory failure EEG and REG changes also increase in intensity. 5. EEG changes with abolition of reactions, scant morphological features and considerable decrease of amplitude may be the passive type of reaction to hypoxia.