Black cardiologists hailed the results after years in which minorities got short shrift in medical studies. Others complained that the drug also might help whites but wasn't tested that way.

The nationwide study is the largest ever done solely on blacks with heart failure. The findings were reported Monday at an American Heart Association meeting in New Orleans and will be published Thursday in the New England Journal of Medicine.

Heart failure affects 5 million Americans, but blacks are 21/2 times more likely to get it. It happens when the heart is too weak to pump effectively, causing fluid to back up in the lungs and leaving people weak and short of breath. Half die within five years of diagnosis.

Earlier research suggested that standard heart failure drugs called ACE inhibitors do not work as well in blacks, and that blacks may have lower amounts of heart-healthy nitric oxide in their blood.

Two chemicals - isosorbide dinitrate and hydralazine - boost this substance, but administering doses separately is complicated.

A Massachusetts biotechnology company, NitroMed, developed a combination pill, BiDil, but the FDA refused to license it because earlier studies involving mostly white patients who got the chemicals separately showed no benefit.

But there were tantalizing signs BiDil helped the few blacks in the studies, and NitroMed won a patent to use it just for them.

The company then launched a study of 1,050 blacks. Half got standard drugs; the rest got those plus BiDil. The study was stopped early when doctors saw BiDil clearly was better.

After roughly two years' use, 6.2 percent of the patients who took BiDil had died versus 10.2 percent who got only standard drugs.

The favorable overall result "virtually ensures FDA approval," because the agency previously told the company that a successful study in blacks would merit it, Dr. M. Gregg Bloche, a Georgetown University lawyer and Johns Hopkins University physician, said in a commentary in the medical journal.

That is "cause for celebration" for blacks, but the company now will have no financial incentive to do a larger trial in whites because its "black-only" patent allows it to sell it that way and keep generic versions from coming the market until 2020, he said.

Others worried that the drug might not be the best choice for every black but that they will automatically be prescribed "the black pill" solely on the basis of skin color.

Dr. Shamir Mehta, a heart expert from McMaster University in Ontario who has done much research on ethnic differences, said the genetic differences among ethnic groups are so small that the drug should probably help whites, too.

The early studies in the 1980s that found no benefit from the two chemicals in whites were done before modern heart failure drugs were available, and that could warrant a new study involving all races, experts noted.

The Food and Drug Administration could approve the drug generally but say it had been tested only on blacks, said Dr. Clyde W. Yancy, a heart specialist at UT Southwestern Medical Center in Dallas and a study participant.

NitroMed's vice president for marketing, B.J. Jones, said the company would submit results and let the FDA decide.