NEW ORLEANS - An experimental drug is the first to substantially and safely improve shortness of breath and other symptoms in people hospitalized with severe heart failure, an epidemic that is growing as baby boomers age, doctors reported Sunday.

Dr. Randall Starling, left, listens while Dr. Marvin Konstam speaks during the American College of Cardiology summit in New Orleans, Sunday, March 25, 2007. [AP]

However, many were disappointed that the drug also did not help people live longer or stay out of the hospital.

"What we really need are therapies that are going to improve the outcome," said Dr. Gregg Fonarow, an American Heart Association spokesman from the University of California at Los Angeles.

He had no role in the study, which was led by Dr. Marvin Konstam of Tufts-New England Medical Center and presented at an American College of Cardiology conference. Results also were published online by the Journal of the American Medical Association and will be in its March 28 issue.

Heart failure occurs when the heart muscle weakens over time and can no longer pump effectively. Fluid can back up into the lungs and leave people panicked and gasping for breath.

About 5 million Americans have the condition. It kills more than 300,000 and accounts for a million hospitalizations each year.

Severely ill heart failure patients need to shed buckets of water, but current treatments either do not cause this fast enough or lead to kidney damage or loss of essential body salts called electrolytes.

A drug that does this better is drastically needed, said Dr. Mariell Jessup, head of the heart failure center at the University of Pennsylvania, who was not involved in the study.

"What we're doing now is not working. These patients come back over and over," she said.

The new drug, tolvaptan, is a first-of-its-kind medication that blocks a hormone responsible for fluid retention.

It was tested on 4,133 severely ill patients throughout North and South America and Europe. They were randomly assigned to receive either the new drug or fake medication in addition to other standard heart failure treatments like diuretics within 48 hours of hospitalization.

Ten months later, the drug made no difference in the rate of death or rehospitalization - a big disappointment. But it significantly improved breathing and reduced swelling and weight because it promoted so much fluid loss.

Side effects mostly involved nuisances like dry mouth and thirst, and no extra risk of death or kidney problems was seen - the main things doctors were worried about.

"This is the first drug that's ever been documented to reduce symptoms and be safe," Konstam said. "As early as one day, taking just one pill, there was an improvement in shortness of breath, which is the No. 1 symptom patients complain about that drives them to the hospital."

Tolvaptan's maker, Otsuka Pharmaceutical Co. of Japan, paid for the study and Konstam is one of its consultants. The company plans to ask the federal Food and Drug Administration to approve the drug sometime this year.

If it gets approved, "we will have another option for patients that will relieve the primary symptom bringing them to the hospital," said Dr. Clyde Yancy of Baylor University Medical Center in Dallas.

He led a study also reported on Sunday of the only drug currently on the market to treat shortness of breath in hospitalized patients with severe heart disease. That drug - Natrecor - looked to be a blockbuster, but many doctors avoid it because of worries that it might raise the risk of death.

The drug's packaging was changed to include more information about the risk of death in 2005.

The new study tested whether regular infusions of the drug on an outpatient basis could prevent death and hospitalizations in about 900 severely ill heart failure patients.

It did not. However, no extra risk of death or kidney problems were seen with the drug.

"I would say those concerns can be lessened," said Yancy, who consults for the drug's maker, Scios Inc., a division of Johnson & Johnson. The company plans to start a very large study of Natrecor later this year. The drug's label says there is not enough information yet to know if the drug brings an increased risk of death.