Heart-failure researchers are testing a provocative hypothesis: whether a technique used by elite athletes to improve endurance can help some of medicine's sickest patients improve their ability to exercise and function in their daily lives.

The technique simulates high-altitude training in which cyclists and other endurance-sport athletes sleep in sealed tents where oxygen levels mimic the thin air at mountain elevations in a bid to improve their performance at normal heights. Now a pilot study is under way to see if thin air is a boon to heart-failure patients as well.

Left to right: Heart patient Felipe Correa-Diaz undergoes high-altitude simulation therapy while Auris Browne and Vivek Bhatia of the Montefiore-Einstein Center for Advanced Cardiac Therapy monitor his progress. Adi Talwar

The idea may seem counter-intuitive. A common symptom of heart failure, a chronic weakening of the heart muscle that compromises its ability to pump blood, is shortness of breath. Patients often have difficulty climbing a flight of stairs or walking a block or two.

But Simon Maybaum, medical director of the Montefiore-Einstein Center for Advanced Cardiac Therapy in the Bronx, N.Y., says the problem in heart failure isn't a lack of oxygen, but poor blood flow. He thinks the physiological changes athletes gain from a "sleep-high" strategy can help improve the ability of heart-failure patients to get more oxygen to body tissue and gain endurance as a result.

"The same changes that occur in an athlete should also benefit people who have cardiac dysfunction," Dr. Maybaum says.

The role of exercise in heart-failure patients is still being studied. Cardiologists say some small studies have shown the benefits of exercise, but it is still an open question whether improved exercise performance dramatically lowers mortality and hospital rates from heart failure.

Dr. Maybaum is principal investigator of a pilot study testing the high-altitude approach. It will enroll 15 people who have stable chronic heart failure. The participants all take medications and use pacemakers but are still limited in the activities they can do. As part of the trial, the patients sit in four-hour sessions inside a tent where the oxygen level is slowly reduced to mimic what is experienced at high altitudes. They start at a level equivalent to 1,500 meters altitude, going up over the course of 10 sessions to 2,700 meters.

In athletes, the regimen can increase red blood cells, improve the efficiency with which these cells transport oxygen, boost lung volume and help muscles use oxygen more efficiently—all things that should help heart-failure patients, too, says Dr. Maybaum.

The trial comes at a time when clinicians and researchers are calling for new thinking about how to treat heart failure. There are an estimated 400,000 new cases every year, and the number is expected to rise further as the population ages. Drugs like ACE inhibitors and beta-blockers used in the treatment of high blood pressure and other cardiovascular diseases have helped in many cases, but they don't work for everyone. "We've hit the wall in terms of what we're able to do for these patients with our current therapies," says Howard Rockman, a cardiologist and professor of medicine at Duke University.

For many patients, current therapies may improve heart function, but fail to increase exercise tolerance. Doctors who treat heart-failure patients say that over time, the fitness level of patients with the disease deteriorates.

"The less they do, the less they can do, so they get even more de-conditioned, and this affects their quality of life,'' says Ileana Pina, a professor of medicine and epidemiology/biostatistics at Case Western Reserve University and chairwoman of the steering committee on an trial funded by the National Institutes of Health that looked at whether exercise improved outcome in heart-failure patients.

One participant in the pilot study is Hector Valentin, a 52-year-old salesman for a flooring company who lives in the Bronx, N.Y. He has suffered from heart failure for six years. He takes medications, has a pacemaker, but tires easily. A baseball fan, Mr. Valentin explains the concept of the study to friends and family by comparing it to a batter who warms up before his turn at bat with a weighted doughnut on the bat.

"The doughnut makes the bat heavier, so when you take it off, the bat feels lighter and it's easier to swing,'' says Mr. Valentin.

A key measure in the trial is one that athletes use to gauge performance: peak oxygen consumption—the rate of milliliters of oxygen per kilogram of body weight the body uses during maximum exertion on a bicycle or treadmill.

Dr. Maybaum says peak oxygen values fluctuate depending on age and fitness levels in the normal population. A collegiate rower might have a peak oxygen-consumption level in the high 40s ml/kg/min. Heart-failure patients' levels range from 10 into the 20s.

When Mr. Valentin enrolled in the study, his peak oxygen value was 13.8 ml/kg/min. After the altitude training, the number went up to 15.9, a significant increase, Dr. Maybaum says.

Mr. Valentin says he feels better after the sessions. The other day, he walked up five flights of stairs; he used to tire after two flights.

"It's hard to tell if the benefits will last," he said, "but I don't feel tired."

Dr. Maybaum hopes that the high-altitude study eventually shows that heart-failure patients can sleep inside tents at home, just as some athletes do, and find it easier to be active and exercise during the day.

Write to Amy Dockser Marcus at amy.marcus@wsj.com