BACKGROUND There is evidence that "inappropriate hypertrophy" of the single left ventricle, which occurs as a result of acute preload reduction, leads to adverse consequences on ventricular function. However, a systematic study of the capability of tissue Doppler imaging (TDI) to assess systolic and diastolic ventricular functions after the Fontan procedure is still missing. METHODS Twenty-four postoperative patients aged 12-33 years were prospectively evaluated with two-dimensional echocardiography equipped with TDI capabilities. Nineteen age-matched normal subjects were selected as controls. Good-quality echoes for the measurement of ejection fractions were available in 21 patients. Ten patients (group 1) had systolic dysfunction (ejection fraction < 50%), and 11 patients (group 2) had normal systolic function. Peak systolic and diastolic wall velocities were acquired from the two-chamber view in the myocardia and mitral annulus. RESULTS Compared with controls, the Fontan patients had a significantly reduced peak systolic velocity at wall and annulus sites. A linear correlation existed between ejection fraction and systolic myocardial velocity from the annular sites. Group 1 patients had lower wall velocities and lower annulus velocities both in systole and diastole. Group 2 patients had preserved systolic velocities but decreased regional and annular early diastolic velocities, suggesting impaired filling. Multiple correlation analysis showed a relation between peak early diastolic mitral velocity and ventricular ejection fraction, mean mitral annular motion at systole, mass/volume ratio, and the number of years post Fontan revision. CONCLUSIONS Myocardial velocities recorded after the Fontan operation give insight into systolic and diastolic ventricular functions. The peak systolic mitral annular velocity correlated well with the ventricular ejection fraction. The peak early diastolic velocity and the ratio between the early and late diastolic mitral annular velocity are reduced and reflect diastolic dysfunction even in the presence of normal systolic ejection fraction.