Few papers on alteration of whole blood viscoelastic properties in patients with congestive heart failure (CHF) have been reported. In this study viscoelastic property parameters were measured in 63 consecutive patients with rheumatic heart disease and CHF. All subjects were divided into four groups according to NYHA classification of heart function. There were 14 class I, 16 class II 20 class III and 13 class IV. Contraves low-shear-30 rheometer was used for measuring the viscoelastic parameters. The results demonstrated that there was no significant difference of these parameters between class I and class II, that the apparent viscosity, AI and eta' in class III were higher than those in class I, and that eta 0.512, eta 5.96 AI, eta', eta" and G' in class III were higher than those in class II. All viscoelastic parameters but eta p in class IV were markedly higher than those in other groups. However, there were no statistically significant difference of eta p among all subjects and nor significant difference of these parameters between male and female were noted. There was a negative correlation between viscoelastic parameters and heart function parameters by pulse Doppler echocardiography (peak flow velocity, stroke volume and cardiac output). The results also showed a significant direct correlation between eta 0.512 AI, and eta" and the heart function parameters mentioned above.