Mitral valvar diseases would be ones in which hemodynamic study was frequently required to follow up patients, regardless of undergoing surgical treatment. Therefore, it would be ideal if hemodynamic study could be done under non-invasive technique. In this respect RI cardiograph (radiocardiograph) seems to be suitable because a needle puncture to inject a dose (10mCi) of radioisotope ((99m)Tc pertechnetate) is only one thing to be done under invasive technique. This study is to show applicability of RCG and to determine criteria for its use. Instrumentation employed for data processing was DAP 5000-2 (Toshiba, Ltd. Tokyo, Japan) and the data obtained were processed by computer. RI dilution curves recorded on the right ventricle, the left lung, the left ventricle were analyzed to obtain following parameters, namely interventricular peak to peak time, down-slope of RI dilution curve of the left lung, and the up- and the down-slopes of RI dilution curves of the left ventricle. Patients studied were 37 ranging from 15 to 64 years of age. Preoperatively, interventricular peak to peak time was prolonged and RI dilution curves of the left lung and the left ventricle were widened. Postoperatively these parameters were resumed to normal or close to normal. Coefficient of correlation (r) of up-slope of the left ventricle to NYHA classification was turned out to be -0.64 and that of down-slope to NYHA to classification was 0.63. It was concluded that the parameters studied, including down-slope and up-slope of RI dilution curves of the left ventricle and down-slope of the left lung, reflected reasonably well hemodynamic alterations of patients with mitral valvar diseases, and that RCG should have great advantage for following up patients with mitral valvar diseases because of its non-invasive technique and ready repeatability.