Although tetralogy of Fallot (TOF) can be repaired surgically, residual lesions that cause abnormal ventricular load can eventually lead to heart failure. Subclinical biventricular dysfunction in these patients may be detected only by using suitably sensitive indexes. The Tei index determined by the pulsed Doppler method enables the measurement of left ventricular (LV) and right ventricular (RV) function. This study was designed to evaluate the biventricular Tei indexes in adults with operated congenital heart disease and to correlate these indexes with cardiopulmonary capacity and neurohormonal activation. Fifty-nine patients with surgically corrected TOF and 52 patients with operated left-to-right-shunt defects were included in the study. Patients with TOF showed significantly greater LV and RV Tei indexes than those with left-to-right-shunt defects (LV Tei index 0.50 ± 0.09 vs 0.34 ± 0.05, RV Tei index 0.37 ± 0.1 vs 0.25 ± 0.06; p <0.0001). Peak oxygen uptake was significantly reduced in the patients with TOF (25 ± 6 vs 32 ± 6 ml·kg⁻¹·min⁻¹, p <0.0001) and was correlated inversely with the LV Tei index (r = −0.61, p <0.0001). N-terminal–pro-brain natriuretic peptide was significantly increased in patients with TOF (150 ± 141 vs 57 ± 39 pg/ml, p <0.0001). In conclusion, in asymptomatic or minimally symptomatic patients with TOF, biventricular dysfunction is detected by the Tei index. Further indexes for heart failure in these patients are increased circulating plasma N-terminal–pro-brain natriuretic peptide and impaired peak oxygen uptake. The combined determinations of these 3 variables enable the identification of congenital heart disease with impaired cardiac function before they become clinically symptomatic.