The medication, called an angiotensin-receptor blocker, or ARB, is a pillar of heart failure therapy, used by about 15% of patients to relax blood vessels and reduce stress on the heart. Until now, doctors have lacked the evidence they needed to determine the most effective dose.

A new study of nearly 4,000 patients, half of whom got 50 milligrams and half of whom got 150 milligrams, found that the higher dose significantly reduced deaths and hospitalizations. The patients were followed for nearly five years.

"We found that the higher dose reduced the death rate by 10%," says Marvin Konstam of Tufts Medical Center in Boston, who reported his findings at an American Heart Association meeting here. Upping the dosage, he says, could prevent one death or hospitalization for every 31 patients over four years.

Standard heart failure treatment guidelines advise doctors to prescribe a diuretic, a beta blocker to ease the heart's workload, and a blood pressure drug called an ACE inhibitor. But many patients can't take ACE inhibitors because of side effects. Those patients are routinely given ARBs.

"From a scientific standpoint," says Raymond Gibbons of the Mayo Clinic in Rochester, Minn., "this is important information that we've overlooked." Gibbons says he will begin shifting his patients to the higher doses.