Left ventricle (LV) systolic dysfunction in repaired tetralogy of Fallot (TOF) has been identified as a risk factor for functional status and adverse outcome. The aims of this cross-sectional followed by a prospective study were: (1) to evaluate the prevalence of LV systolic dysfunction in a large cohort of adults with repaired tetralogy of Fallot, (2) to test the relationship between LV systolic dysfunction and other known risk factors and (3) to evaluate the impact of LV systolic dysfunction on adverse cardiac events. In a multicenter study, 237 adults repaired TOF (58 % males, age 30 ± 10 years) were evaluated by cardiac magnetic resonance (CMR). Demographics, surgical history, ECG, Echo-Color Doppler and follow-up data were recorded. LV was dilated (Z value >2) in 16 patients (6 %), however 56 patients (23.6 %) had a reduced LV systolic function left ventricle ejection fraction (LVEF) (Z value <−2). Patients with LV systolic dysfunction were mainly males (82 %), had reduced right ventricle ejection fraction (RVEF), and higher right and left Late Gadolinium Enhanced scores. In a multivariate regression analysis male gender and RVEF resulted to be independent factors associated to LV systolic dysfunction. Atrial arrhythmias were the main adverse cardiac event at the follow-up and were associated to higher biventricular volumes and lower biventricular ejection fraction (EF); however multivariable analysis identified age, right ventricle end-diastolic volume (RVEDVi) and tricuspid regurgitation as independents factors associated to atrial arrhythmias. At long term follow-up at least ¼ of repaired TOF has LV dysfunction. Lower LVEF is associated to male gender and lower RVEF.