Background Some patients with heart failure (HF) may have a marked improvement in left ventricular ejection fraction (LVEF) after long-term β-blockade. We compared the clinical characteristics and the prognosis of these patients with those of other patients. Methods One hundred seventy-one patients with chronic HF were assessed before and after 9 to 12 months of maintenance therapy with metoprolol or carvedilol. Results Thirty-eight patients (22%) showed an increase in their LVEF ≥15 units (from 20% ± 8% to 43% ± 10%). Compared with the other patients (LVEF change from 21% ± 7% to 26% ± 9%, P <.0001 for differences between groups), these patients also had a greater decline in the left ventricular end-diastolic volume (from 175 ± 74 mL/m² to 113 ± 36 mL/m²) and in the right atrial, mean pulmonary artery, and pulmonary wedge pressures, with a greater increase in the cardiac index, stroke volume index, stroke work index, and maximal functional capacity. Their long-term prognosis was excellent, with a 2-year cumulative survival rate of 95%, versus 81% for the other patients, and a hospitalization-free survival rate of 73%, versus 50% for the other patients (all P <.05). By means of multivariate analysis, only the nonischemic cause of HF and the mean arterial pressure at baseline were independently associated with an increase of ≥0.15 in LVEF. Conclusions Patients who show a marked improvement in their LVEF after long-term β-blockade have an excellent prognosis and have a high prevalence of nonischemic HF and a higher blood pressure at baseline. (Am Heart J 2003;145:292-9.)