The employment of gamma-ray scintillation camera with the use of short-lived radioisotopic pharmaceuticals, sucu as 99mTc sodium pertechnetate, have enabled us to perform RI (radioisotopic) angiocardiography. Although conventional cardiac catheterization or angiocardiography using contrast media have been an important diagnostic tool, they may carry some risks or serious complications. The author investigated on RI angiocardiography in twelve normal and twenty five patients with cardiovascular diseases in an effort to evaluate its diagnostic value. The results obtained with this study are as follows; l. In normal subjects, the scintillation camera transit time of arm-to-right heart was found to be 2. 1¡¾0. 67 seconds, right heart-to-lung 1. 5¡¾0. 40 seconds and lung-to-left heart 3. 5¡¾0. 86 seconds. 2. Transformation or displacement of the heart and the great vessel are easily discriminatal by RI angiocardiography. Both in the cases with tricuspid atresia and tetralogy of Fallot, ventricular septal defects are well recongnized by sequential RI angiocardiography. 3. It is also helpful in determinining the site and extent of obstruction, and estimatiing the postoperative course both in the cases with superior vena cava syndrome and pulmonary stenosis. 4. Pericarditis with effusion is readilly diagnosed by RI angiocardiogram showing characteristic "dead space" between intracardiac and intrapulmonary radioactivity. 5. It was found that the diagnostic accuracy of this study was 78. 4%. It is concluded that above results obtained are useful and accurate enough for the diagnostic screening methode for clinical practice.