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Vector flow mapping (VFM) enables direct visualization of flow pattern and estimation of flow volume. The aim of this study was to determine its accuracy in the quantification of pulmonary regurgitation (PR) in congenital heart patients after repair of right ventricular (RV) outflow obstruction.This study comprised two parts: (1) validation of VFM in the quantification of PR in patients with repaired tetralogy of Fallot by cardiac magnetic resonance and (2) clinical application of VFM to determine PR in patients after biventricular repair of pulmonary atresia and stenosis with intact ventricular septum. PR was quantified by calculation of VFM-derived pulmonary regurgitant ratio (PRVFM), defined as ratio of backward to forward flow volume.Coefficients of variations for intra- and interobserver variability in the measurements of PRVFM were 7.0% and 10.4%, respectively. Fourteen patients with repaired tetralogy of Fallot aged 31.3 ± 7.3 years were studied. Their PRVFM correlated strongly with cardiac magnetic resonance–derived PR fraction (r = 0.95, P < .001) and RV end-diastolic volume (r = 0.84, P < .001). In the second part, 14 patients with pulmonary atresia with intact ventricular septum aged 25.6 ± 6.0 years, 14 patients with pulmonary stenosis aged 24.2 ± 7.0 years, and 14 healthy control subjects were studied. PRVFM was found to increase across groups of subjects with absent (4.6 ± 3.3%), mild (11.1 ± 7.1%), moderate (29.6 ± 7.8%), and severe (50.1 ± 8.2%) PR as defined semiquantitatively by color flow mapping. Furthermore, PRVFM correlated strongly with the ratio of PR color jet to width of RV outflow (r = 0.92, P < .001).VFM is a reproducible technique for accurate quantification of PR in congenital heart patients after repair of RV outflow obstruction.Serial evaluation for progression of pulmonary regurgitation is important in the long-term follow-up of congenital heart patients after repair of right ventricular outflow obstruction.Vector flow mapping is a new color Doppler-based echocardiographic technology that enables visualization of blood flow as velocity vectors and determination of flow volumes.This study validates the accuracy of vector flow mapping-derived pulmonary regurgitant ratio against cardiac magnetic resonance-derived pulmonary regurgitant fraction in patients with repaired tetralogy of Fallot.Clinical application of vector flow mapping to other groups of congenital heart patients, including those after biventricular repair of pulmonary atresia with intact ventricular septum and pulmonary stenosis, for quantification of pulmonary regurgitation is further shown to be feasible.