Among the main components of the Triogy of Fallot, pulmonary stenosis, right ventricular hypertrophy and right to left shunt through the ASD or patent foramen ovale, pulmonary stenosis is the most important factor. Due to the pulmonary stenosis, right ventricular and right atrial pressure are increased and this results in venoarterial shunt across the ASD or patent foramen ovale and in cyanosis. Radiological findings of eight cases of the Trilogy experienced at the Department of Radiology, Seoul National University Hospital, were analysed with their clinical findings. The summerized results were as follows: 1. Male to female ratio was 4 : 4, and the age of the patients was distributed between 6 year and 31 year. The common symptoms and signs of the patients were cyanosis, dyspnea on exertion, phalangeal clubbings and grade III-IV systolic murmur. In most cases, the clinical diagnosis was the Tetralogy of Fallot. 2. The characteristic findings of right heart catheterization were (1) right to left transatrial shunt, (2) increased right ventricular pressure without transventricular shunt, and (3) abrupt decrease of pulmonary arterial pressure. In all eight cases, the right ventricular pressure was elevated more than 100mmHg, and in six cases, the right ventricular pressure was elevated more than systemic blood pressure. 3. In chest PA view, six of eight cases were presented mild cardiomegaly, however in two cases, the cardiothoracic ratio was under 50%. Important chest PA findings were prominent pulmonary conus, decreased pulmonary vascularity and left atrial enlargement. In all cases, the cardiac apex was not elevated. 4. In right heart cardioangiograms, the right ventricular cavity was small except one case, and infundibular hypertrophy of right ventricle was present in all cases. The left lateral view of right heart cardioangiogram was very useful in the evaluation of the infundibular hypertrophy, pulmonary valvular stenosis and poststenotic dilatation of p lmonary artery, Especially the stenosis, thickening and doming of the pulmonary valve was beautifully demonstrated in the left lateral view of right heart cardioangiogram. 5. The right heart cardioangiogram, with right heart catheterization, was essential in diagnosis of the Trilogy of Fallot.