A method is described for quantifying pulmonary regurgitation. This method is based on a comparison of the right and left ventricular stroke volumes which are determined from biplane angiocardiograms. These techniques were applied to study 18 postoperative patients with tetralogy of Fallot. In patients with an outflow patch, regurgitant fraction was well correlated with regurgitant area. The RVEDV/LVEDV ratio was also correlated well with regurgitant fraction. Although majority of patients maintained normal RV ejection fraction, there were small number of patients with large regurgitant fraction and decreased RV ejection fraction.