NEW ORLEANS — Exercise can do a lot of good for most people, but it apparently isn't much help to those with heart failure.

The study — the largest ever of exercise in patients whose hearts don't pump enough blood — left many doctors disappointed. Results were reported last Tuesday at an American Heart Association conference.

Although there were some encouraging trends and clear benefits for certain people, exercise failed to deliver on the main goal — keeping people out of the hospital and improving their survival rates.

"It's a shame," said Dr. Harlan Krumholz, a quality-of-care researcher at Yale University who had no role in the study. "Exercise is not that magic elixir that we had hoped," at least for these patients.

In the United States alone, about five million have heart failure. It kills more than 300,000 of them and accounts for a million hospitalisations each year. Those numbers are expected to grow as the US population gets older.

The condition occurs when the heart muscle weakens over time and can no longer pump effectively. Fluid can back up into the lungs, leaving people gurgling and gasping for breath as they struggle to climb stairs or walk around the block.

Exercise has long been known to prevent heart disease and help heart attack patients recover, but smaller, previous studies have made conflicting findings about whether it helps heart failure patients or if it is even safe.

Doctors had hoped exercise would prove as effective as drugs, sparing patients the cost and potential side effects.

The study involved 2,231 people with moderate heart failure in the United States, Canada and Europe. It was led by Dr. Christopher O'Connor at Duke University.

All of the patients were getting optimal medical care, with more than 90 percent on an ideal mix of medicines. Those who needed them also had implanted heart devices to maintain good rhythm.

They were randomly placed in two groups — one given usual care and the other usual care plus an exercise training program. Exercisers were given 36 supervised training sessions lasting half an hour three times a week. After 18 such sessions, they were given a treadmill or an exercise bike to use at home, for five 40-minute sessions each week.

Three months into the study, only half were exercising at least three times a week for 40 minutes. After one year, only one-fourth were exercising five times a week.

The fact so few stuck with the exercise programme made it difficult to show a positive result, O'Connor said.

There were 796 deaths or hospitalizations among those getting usual care and 759 in the exercise group — a statistical draw.

However, after doctors adjusted for factors like how long people were able to tolerate exercise, how badly damaged their hearts were and rates of depression, they did find a modest but significant benefit for exercise.

"It's disappointing," said Dr. Robert Eckel, a former heart association president and an exercise specialist at the University of Colorado at Denver.

"We all would have liked to see a huge benefit to exercise," said Dr. Lawton Cooper, medical officer at the National Heart, Lung and Blood Institute, which paid for the study.

Still, for most people, "it is worth your while," Cooper said. "We know there are all kinds of benefits of exercise."

Among them: quality-of-life improvements, said Dr. Ann Bolger, a heart failure specialist at the University of California in San Francisco.

"Just the fact that it's safe is a huge deal," she said. "Patients want to be in control and to be active," and this shows them they can.