Background: Friedreich's ataxia (FRDA) is a cerebellar ataxia due to GAA repeat expansions in the FXN gene, and in affected patients, lower left ventricular ejection fraction (LVEF) leads to poorer prognosis. We aimed to identify patients likely to develop worsening LVEF at an early stage. Methods: We included 115 FRDA patients aged 30 ± 10 years with 620 ± 238 GAA repeats on the shorter allele and disease onset of 15 ± 7 years. Results: At baseline, left ventricular (LV) hypertrophy was present in 53%, with LVEF 65 ± 7%, LV end diastolic diameter (LVEDD) 43 ± 5 mm, septal wall thickness (SWT) 11.8 ± 2.7 mm, and posterior wall thickness 11.1 ± 2.5 mm. After a mean follow-up of 13 ± 6 years, LVEF ≤ 50% was observed in 12 patients. The main determinants of LVEF ≤ 50% were GAA repeat number on the shorter allele (odds ratio [OR] 1.007, 95% confidence interval [CI] 1.003-1.012, p = 0.002), LVEDD (OR 1.217, 95% CI 1.058-1.399, p = 0.006), and SWT (OR 1.352, 95% CI 1.016-1.799, p = 0.04). High-risk patients were predicted 5 years before LVEF ≤ 50% occurred: area under the curve of 0.91, 95% CI 0.85-0.97. Patients with GAA repeats > 800 were categorized as high risk, patients with 500 < GAA < 800 were high risk if LVEDD was ≥ 52.6 mm and SWT was ≥ 13.3 mm, and patients with GAA < 500 were low risk if LVEDD was < 52.6 mm and SWT was < 13.3 mm. Conclusions: Echocardiographic follow-up combined with size assessment of GAA repeat expansions is a powerful tool to identify patients at high risk of developing LV systolic dysfunction up to 5 years before clinical symptoms. Further studies are mandatory to investigate if these patients would benefit from cardiac interventions.