Since the complication of tricuspid insufficiency has often been experienced at open heart surgery, the necessity of the preoperative establishment of its diagnosis was keenly felt. However, it was in many cases difficult to make an exact diagnosis of tricuspid insufficiency preoperatively on clinical features or by other diagnostic procedures heretofore in use. Thus, the present author has made it a clue to its diagnosis to determine the regurgitation visually by conducting right ventricular angiography and compare it with the preoperative findings obtained. Materials and Methods 1) On 382 cases out of the patients with heart disease or disease of the chest treated at our Institute for Cardiovascular Diseases, Kurume University, angiocardiography of the right ventricle was performed. The presence of regurgitation of a contrast medium to the right atrium was examined thoroughly and its degree was divided into Grade 0, I, II, and III. 2) On 27 cases with no shunt in which tricuspid insufficiency was demonstrated at open heart surgery at the Second Department of Surgery, Kurume University, and on 15 cases of acquired heart diseases without having tricuspid insufficiency, 42 cases in total, the degree of regurgitation, clinical findings, phonocardiograms, electrocardiograms, chest X-rays, and the hemodynamic examination were investigated. More-over the relation between restenosis of the mitral valve and tricuspid insufficiency and the nature of the tricuspid valve recognized at operation or at autopsy were discussed. 3) On 64 cases in which right ventricular angiography was first conducted and then the presence of tricuspid insufficiency and its grade were identified at operation the findings obtained at angiography and those at operation were comparatively studied. At angiography, an angiographic catheter NIH, 7F-9F, was introduced from the brachial vein or the great saphenous vein. Introduction of the catheter into the right ventricle was carried out under the fluoroscope and ascertained by the measurement of pressure curve as well as by the blood letting. In addition, the site of the tip of the catheter at right ventricular angiography was compared with the angiographic findings. As a contrast medium a 76 per cent urografin of 1.0-1.5 ml/kg was employed and injection was made at pressure of 7-10kg/cm2 by using an Elema-Schoenander's automatic injection unit. Electrocardiograms, the injection time and the phase of photography were recorded simultaneously.