Some recent trials have shown that angiotensin-converting enzyme (ACE) inhibitors and/or β blockers can improve left ventricular (LV) function and decrease LV mass in patients with idiopathic dilated cardiomyopathy (IDC). We assessed the prevalence and predictors of patients with IDC that showed marked reverse remodeling (a decrease in LV end-diastolic dimension ≥5 mm to a final LV end-diastolic dimension ≤55 mm and an increase in percent LV fractional shortening ≥5% to a final percent fractional shortening of ≥25% and a decrease in LV mass ≥10%) after 2 years of intensive therapy with ACE inhibitors and/or β blockers. In 78 patients with IDC (mean age 51 ± 14 years), the clinical, echocardiographic, hemodynamic, laboratory, and endomyocardial biopsy data were evaluated at diagnosis and serial echocardiography was performed for 2 years. After 2 years of therapy, 20 of 78 patients (26%) showed marked reverse remodeling. Multivariate analysis revealed that higher systolic blood pressure (135 ± 17 vs 120 ± 16 mm Hg, p <0.001) and lower pulmonary arterial wedge pressure (7 ± 3 vs 12 ± 8 mm Hg, p <0.01) at diagnosis were independent predictors of reverse remodeling. Then, we further analyzed the prognosis of these patients for a mean of 50 ± 32 months; 5-year survival (p <0.02) and event-free rates (p = 0.001) were better in patients with reverse remodeling than in patients without reverse remodeling.