Right ventricular ejection fraction (RVEF) assessed by cardiac radionuclide angiography has been applied to evaluate ventricular function such as ischemic, valvular and congenital heart disease. Using this modality, previous reports also suggest that there is good correlation between RVEF and mean pulmonary arterial pressure (mPA) from catheterization findings in mitral valvular disease and chronic obstructive lung disease. In this study, cardiac RI angiography were performed on 33 adult patients with atrial septal defect (ASD). RVEF is not so good correlation (r=-0.42) with mPA, but in cases within pulmonary to systemic ratio (Qp/Qs) less than 2.0 limits, there is good correlation between RVEF and mPA (n=9, r=-0.71). As a conclusion, in ASD, both afterload assessed by mPA and preload assessed by Qp/Qs decrease RVEF. (author).