Two patients operated upon for tricuspid atresia by Glenn operation are presented. They were five years old and four years old females who were cyanotic shortly after birth, and remained cyanotic. On physical examination, cyanosis on digits and lips, clubbing of fingers, thrill and grade III systolic murmur on 4th I.C.S. along left sternal border were noted. In the first case, chest roentgenograms showed normal pulmonary markings, and the electrocardiogram was interpreted as showing left ventricular hypertrophy with left axis deviation and peaked P-wave in lead IL Right heart catheterization showed high pressure in right atrium and the catheter tip was easily inserted into the left atrium through septal defect. In the second case, chest roentgenograms showed cardiomegaly with sparse pulmonary vascular markings and narrowed vascular pedicle, and the electrocardiogram showed left ventricular hypertrophy with some element of right atrial hypertrophy. Angiocardiogram showed changes characteristic of tricuspid atresia, including "right ventricular window" The findings of right heart catheterization were similar to those of first case. On the basis of these observations, they were diagnosed as tricuspid atresia, and Glenn operation was performed. Normal position of great vessels combined with ventricular septal defect and pulmonary stenosis were noted on the first case, and on second case, transposition of great vessels was additional finding. Postoperative course was uneventful and favorable outcome was obtained.[KTCS 1973;1:63-68]