The drug's main benefit is decreasing shortness of breath in heart-failure patients, often the most debilitating symptom of the illness.

Hospitals are not paid more when they help keep a heart-failure patient from coming back to the hospital, for example.

It is still beneficial for many, but not for heart-failure patients.

The drug was meant for heart-failure patients who are so ill that they arrive at emergency rooms barely able to walk or breathe.

The company reasoned that the drug's effect on nitric-oxide deficiency, more common in black heart-failure patients than in nonblacks, might make it especially suited to them.

The kind of patient that could benefit the most is the heart-failure patient who has severe limitations and no definitive treatment options left.

Normal T-wave signals are seen as a reliable predictor that a heart-failure patient is not at risk of having a heart attack in the next year.

In a study of the drug last year sponsored by the manufacturer, 1,050 African-American heart-failure patients showed a 43 percent reduction in mortality.

Now, when doctors prescribe those drugs for heart-failure patients, only about half respond.

Dr. Liggett suggests it might make sense to offer genetic testing to relatives of heart-failure patients who have the altered genes.