Metoprolol is a cardioselective beta blocker that has been shown to improve left ventricular function and symptoms of congestive heart failure (CHF) and also to decrease the number of hospitalizations due to CHF. However, the effects of metoprolol on mortality in patients with CHF have yet to be determined. Accordingly, the Metoprolol CR/XL Randomized Intervention Trial in Heart Failure (MERIT-HF) has been designed to investigate the effect of once-daily dosing of metoprolol succinate controlled release/extended release (CR/XL) when added to standard therapy in patients with CHF. A total of 3,200 patients will be recruited for this international, double-blind, randomized, placebo-controlled survival study. The 2 primary objectives of MERIT-HF are to determine the effect of metoprolol CR/XL on (1) total mortality and (2) the combined endpoint of all-cause mortality and all-cause hospitalizations (time to first event). Eligible patients are 40-80 years old, with a reduced left ventricular ejection fraction (< or =0.40) and symptoms of CHF (New York Heart Association functional classes II-IV). After a 2-week placebo run-in period, an optimal allocation procedure will be used to randomize patients in a 1:1 ratio to metoprolol CR/XL or matching placebo. After an initial titration phase starting with 12.5 mg or 25 mg once daily (depending on functional class), the target dose will be 200 mg in all patients who tolerate this dose. The mean follow-up is estimated to be 2.4 years. The study data will be analyzed on an intention-to-treat basis. An Independent Safety Committee will monitor the safety aspects of the trial, and an Independent Endpoint Committee will classify all endpoints.