Background The therapeutic strategy for pulmonary atresia (PA) and severe pulmonary stenosis (PS) with intact ventricular septum is controversial. Recent improvements in prenatal detection necessitate the identification of predictors of outcome for appropriate counseling and prenatal management planning. Methods and Results Echocardiograms of 18 fetuses antenatally diagnosed with PA (n=14) and PS (n=4) were reviewed and the total cardiac dimension (TCD) and tricuspid valve diameter (TVD) were measured. The right ventricular end-diastolic volume (RVEDV) was calculated from the right ventriculogram of the neonatal period by the percentage of the predicted normal value (%RVEDV). There was a positive correlation between TVD/TCD and %RVEDV (p<0.001). As the initial treatment, balloon atrioseptostomy was performed in 13 cases of TVD/TCD <0.26. As the final treatment, patients with TVD/TCD <0.17 underwent or were planned for the Fontan procedure. Patients with TVD/TCD >0.21 underwent or were planned for biventricular repair. Patients whose TVD/TCD was between 0.17and 0.21 underwent or were planned for 1.5 ventricular repairs. Conclusion TVD/TCD is a useful index for selecting the postnatal initial treatment for PA/PS and to predict the final status of the fetus. Prenatal detection and prediction of the future status is helpful for family counseling. Furthermore, it will help to decide the postnatal management prenatally. (Circ J 2008; 72: 1471 - 1475)