A total of 126 cardiac output values were recorded by the thermodilution and impedance cardiography methods in 8 adult mongrel dogs. The mean cardiac output in Litres/min, standard deviation and standard error of the mean percent (SEM%) of the thermodilution and impedance methods were 1.75, ± 0.92, 4.7% and 1.5, ± 0.59 and 3.5% respectively. Results show that the mean values of cardiac output measured by thermodilution and the impedance methods are the same (T test, Not significant at p<0.05). The reproducibility of the thermodilution method is poorer than that of the impedance method, as it is given by the SEM%. The correlation coefficients found for cardiac output and stroke volume were 0.61 and 0.76 respectively. The results of this study encourage the use of the impedance method in cases of low cardiac output.