Carvedilol and metoprolol are beta(1)-adrenoceptor antagonists that decrease mortality in heart failure. It is not clear whether the ancillary properties, which carvedilol has but metoprolol does not have, contribute to the beneficial effect. The Carvedilol Or Metoprolol European Trial (COMET) compared metoprolol tartrate (mean daily dose 85 mg) and carvedilol (41.8 mg) in patients with heart failure. All-cause mortality was less in the carvedilol than the metoprolol group, indicating that at these doses, carvedilol has a mortality benefit over metoprolol. However, the beta(1)-adrenoceptor blocking activity of metoprolol tartrate (assessed by a decrease in heart rate) was slightly less than with carvedilol in COMET and less than that observed in previous mortality studies with metoprolol, suggesting that the use of metoprolol tartrate was not optimal in COMET.