Aim of this prospective study was to evaluate longitudinal systolic left ventricular (LV)-right ventricular (RV) interaction using M-mode compared to magnetic resonance imaging (MRI) data in 146 pediatric and adults with operated tetralogy of Fallot (TOF). We determined biventricular measures of longitudinal M-mode echocardiography [i.e., tricuspid annular plane systolic excursion (TAPSE); the mitral annular plane systolic excursion (MAPSE)] compared to longitudinal function parameters using MRI. M-mode data were compared to established normal z-score values. We found a good correlation between MAPSE and LVEF values (r = 0.788; p < 0.001). Correlations between MRI derived MAPSE and M-mode guided MAPSE (r = 0.879, p < 0.001), and between MRI derived TAPSE and M-mode guided TAPSE were significant (r = 0.780, p < 0.001). While the LVEF was normal in patients with a normal RVEF, the LVEF was decreased in patients with significantly reduced RVEF. Patients with a significantly dilated RV (RVEDVi > 150 ml/m(2)) showed a significantly reduced mean MAPSE of 1.30 ± 0.26 cm. LV longitudinal function decreases below -2 SD of normal MAPSE z-score values after a mean of 22 postoperative years. Our data confirm progressive adverse RV-LV interaction in the long-term follow-up of TOF. We show that simple M-mode measurement of the longitudinal LV function (i.e. MAPSE) is a sufficient surrogate for estimation of LVEF. Therefore determination of the MAPSE is a helpful additional tool for LV systolic function assessment late after TOF repair.