BACKGROUND: Atrial flutter-related tachycardiomyopathy (AFL-TCM) is a rare and treatable cause of heart failure. Little is known about its epidemiology and long-term prognosis. Our aims are to determine the prevalence, predictors and outcomes of AFL-TCM. METHODS AND RESULTS: A total of 1269 patients were referred for radiofrequency ablation of AFL between January 1996 and September 2014; 184 had reduced left ventricular ejection fraction (LVEF <40%). At 6 months after AFL ablation, 103 patients (8.1% of the population, 56% of patients with baseline LVEF <40%) had marked LVEF improvement: these were considered to have AFL-TCM. Patients with persisting reduced LVEF were considered to have systolic dysfunction unrelated to AFL. Patients were followed for a median (percentile25-75 ) of 1.15 (0.4-2.8) years. Patients with AFL-TCM were younger, had lower prevalence of ischaemic cardiomyopathy and used less antiarrhythmic drugs than patients with systolic dysfunction unrelated to AFL. In multivariable analysis, ischemic cardiomyopathy [odds ratio (OR) = 0.32, 95% confidence interval (CI) 0.15-0.68) P = 0.003] and prescription of antiarrhythmic drug before ablation [OR = 0.41, 95% CI 0.20-0.84, P = 0.02] were significantly associated with a lower probability of LVEF improvement during follow-up. Patients with AFL-TCM had similar survival to patients without systolic dysfunction at baseline [hazard ratio (HR) = 0.96 95% CI 0.34-2.65, P = 0.929], whereas patients with systolic dysfunction unrelated to AFL had higher mortality rates compared with patients without systolic dysfunction at baseline [HR = 2.88, 95% CI 1.45-5.72, P = 0.002]. CONCLUSIONS: Marked LVEF improvement was observed in 56% of patients with baseline LVEF <40% at 6 months after ablation. These patients had similar survival to patients without baseline systolic dysfunction, whereas patients who remained with LVEF <40% had a threefold increase in mortality rates.