Arrhythmic risk stratification in idiopathic dilated cardiomyopathy (IDC) remains a major concern. As the ventricles remodel in time, risk factors for arrhythmic death may change. A cohort of 710 patients with idiopathic dilated cardiomyopathy, without previous ventricular arrhythmias, was retrospectively studied to understand how risks vary in time. The primary end point was a composite of sudden cardiac death, ventricular fibrillation, sustained ventricular tachycardia, and appropriate implantable cardioverter-defibrillator interventions. The prediction of the arrhythmic outcome was assessed dynamically through landmark analysis. Patients were assessed at baseline, short term (12 months, interquartile range 6 to 18), and long-term (72 months, interquartile range 60 to 84). The strongest risk predictors at each evaluation were combined in 3 multivariate models. During a median follow-up of 102 months, 80 patients (11%) experienced the primary end point. At baseline, QRS duration (p = 0.008), disease duration (p <0.001), and mitral regurgitation (p = 0.010) were significantly associated with the primary end point. The 12 months' landmark model included disease duration (p = 0.049), syncope (p = 0.005), New York Heart Association classes III and IV (p = 0.02), and indexed left ventricular end-diastolic volume (p = 0.001). Finally, the 72 months' landmark model combined the indexed left ventricular end-diastolic volume (p = 0.048), the left ventricular ejection fraction (p = 0.008), and the left atrial area (p = 0.001). All the 3 models provided a satisfactory accuracy (area under the curve ranging from 0.76 to 0.82, p <0.001). With an implantable cardioverter-defibrillator, the natural course of the disease influences the effect of arrhythmic risk factors overtime. Different predictors should be considered for the risk stratification according to the timing of assessment. Impaired left ventricular ejection fraction was significantly associated with major arrhythmias only in the long term.