The aim of the study was to assess echocardiographic measurements of right ventricular function in 24 patients aged 10.7 to 28.9 years (mean 18.9 years) receiving the Mustard baffle repair for transposition of the great arteries. Right ventricular ejection fraction (RVEF) from single-plane areas and area length volumes, pulsed Doppler mean aortic acceleration, and tricuspid annular plane systolic excursion were correlated with first-pass radionuclide RVEF. The mean radionuclide RVEF was 39%, the mean echocardiographic apical four-chamber RVEF was 41%, and the mean short-axis RVEF was 37%. Echocardiographic apical four-chamber right ventricular end-diastolic volumes were 102 +/- 24 ml/m2, and RVEF interobserver and intraobserver correlation coefficients were 0.73 and 0.81, respectively. Radionuclide and echocardiographic RVEF correlation coefficients were short axis, 0.40; apical four-chamber, 0.24; average four-chamber and short axis, 0.38; mean aortic acceleration, 0.26; and tricuspid annular plane systolic excursion, 0.06. The range of echocardiographic right ventricular volumes for young adults receiving the Mustard repair is established allowing serial observation of dilatation. However, simple and reliable echocardiographic prediction of RVEF remains elusive in this age group.