For the purpose of avoiding postoperative massive pulmonary insufficiency after transannular outflow tract reconstruction in patients with tetralogy of Fallot, we have used monocusp bearing outflow patch since June 1983. Right heart catheterization and pulmonary arteriography were performed in 7 patients among the total 11 patients corrected with monocusp bearing outflow patch during postoperative 14th day to 22nd day. Particular attention was paid to the evaluation of the pulmonary valve competence, and the results were; 1.One patient died of acute renal failure secondary to low cardiac output and the operative mortality was 9.1%. 2.The average PRV/FA ratio was 0.491 and the average systolic pressure gradient between right ventricle and pulmonary artery was 17.7mmHg. The average Qp/Qs was 1.13. 3.Inspite of using monocusp bearing outflow patch, the hemodynamic and pulmonary arteriographic results were unsatisfactory in respect to pulmonary valve competence.