Background: Minimally invasive robot-assisted cardiac surgery is generally performed nowadays. To avoid the interference of a superior vena cava (SVC) cannula during surgery, it should be inserted before the operation. The position of this cannula is very important because it can cause poor venous drainage during operation. The proper position of the SVC cannula was investigated in the present study. Methods and Results: The position of the SVC cannula using the transesophageal echocardiography (TEE) and chest X-ray in 45 patients was ascertained. The distances from the SVC cannula tip to the carina, sternal end of the right clavicle and the lower margin of the T4 vertebral body on chest X-rays were measured. The mean depth of the SVC cannula was 142.0±11.6 mm. The correlation coefficients of cannula depth with sex, weight and height were 0.519, 0.399 and 0.382, respectively. Conclusions: The appropriate depth of an SVC cannula has weakly positive relationships with sex, weight and height. The results of the present study suggest that chest X-rays might be necessary to confirm the appropriate location of the cannula and that TEE might be the method of choice for correct positioning of the SVC cannula in minimally invasive robot-assisted cardiac surgery. (Circ J 2010; 74: 284-288)