Tricuspid regurgitation was evaluated in 133 patients with tetralogy of Fallot after corrective operations for a real-time Doppler flow imaging system. Moderate or severe tricuspid regurgitation was found in 15% (10/66) of patients in whom the ventricular septal defect was closed through the right atrium and tricuspid valve, 13% (2/15) through the pulmonary artery, and 25% (13/52) through the right ventricle. These differences were not significant. Right ventricular systolic pressure was significantly higher (66 +/- 27 mm Hg) in patients with moderate or severe tricuspid regurgitation (group A) than in patients with mild or no tricuspid regurgitation (group B) (41 +/- 13 mm Hg) (p less than 0.01). Right ventricular end-diastolic pressure was significantly higher in group A (7.7 +/- 2.2 mm Hg) than in group B (6.1 +/- 2.9 mm Hg) (p less than 0.01). Significant pulmonary regurgitation (angiographic grades 3/4 to 4/4) was more frequent in group A (8/18; 44%) than in group B (14/64; 22%) (p less than 0.05). Residual ventricular septal defect (pulmonary/systemic flow ratio greater than 1.3) was also more frequent in group A (5/18; 28%) than in group B (0/64; 0%) (p less than 0.01). Right ventricular end-diastolic volume was significantly higher in group A (202% +/- 79% of the normal right ventricle) than in group B (158% +/- 38% of normal) (p less than 0.01). Thus significant tricuspid regurgitation was associated with high right ventricular systolic pressure, high right ventricular end-diastolic pressure, and significant pulmonary regurgitation and residual ventricular septal defect, which increased the right ventricular end-diastolic volume. Operative procedure for closing the ventricular septal defect was not related to the development of significant tricuspid regurgitation.