Objective: To compare cardiac outputs (CO) measured by a transesophageal Doppler ultrasound technique (TED, Hemosonic 100[Superscript TM], Arrow Int) and CO measured by thermodilution (TD) in anesthetized dogs. Design: Interventional studies. Settings: Veterinary Teaching Laboratory-Iowa State University. Animals: The study included 10 canines weighing from 18.5 kg to 32.5 kg. Set criteria for inclusion were adequate body size of the dogs for placement of the esophageal probe (body weight>18.5 kg) and stable anesthesia maintenance period. Interventions: Simultaneous TED and TD measurements of CO were obtained during initial baseline period. The baseline CO was then altered by constant rate intravenous infusion of dobutamine, dopamine and norepinephrine; and by caudal vena cava occlusion. Results: Each measurement of CO allowed a comparison of TED and TD values. Forty-nine CO paired comparisons were made with the CO ranging from 0.73 l/min to 10.9 l/min (obtained by TD). Simple linear regression was used to determine the correlation between the two techniques (rà ²=0.53). Bland and Altman statistical method was used for assessing agreement between the two methods. The difference between the TD and TED was 0.82 l/min (bias) and SD was 1.63 l/min. At baseline and low CO levels (caudal vena cava occlusion) the correlation coefficient (rà ²) was 0.77 and at high CO levels (dobutamine, dopamine and norepinephrine infusions) the correlation coefficient (rà ²) was 0.45. Conclusion: The TED might be a useful method for detecting low CO trends and aid in determining the cause of hypotension.