The research included more than 82,000 men between the ages of 45 and 69. Those who spent more time being sedentary outside of work hours, even if they exercised, had a higher risk for heart failure, reported the researchers from Kaiser Permanente Southern California.

"Men with low levels of physical activity were 52 percent more likely to develop heart failure than men with higher levels of physical activity," said study author Deborah Rohm Young, a senior scientist at Kaiser Permanente in Pasadena, Calif.

Young said those who spent at least five hours per day sitting were 34 percent more likely to develop heart failure than those who spent less than two hours a day sitting. The research is published in the January issue of Circulation: Heart Failure.

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The scientists used data from a large study called the California Men's Health Study. None of the men had heart failure at the start of the study.

"We looked at baseline information on a questionnaire about physical activity and sitting time outside of work," said Young, who noted that the men were followed for up to a decade. Their exercise levels were calculated in a way that tallied how much energy the body uses. The researchers also tracked how many hours a day the men were sedentary.

"Those who had low physical activity -- who sat a lot and got little exercise -- were more than twice as likely to have heart failure compared to those who were active and had not very much sitting time outside of work," Young explained.

Heart failure is the inability of the heart muscle to effectively pump blood throughout the body, said Young. It affects 5.7 million Americans -- mostly older people. Approximately 20 percent of adults will be diagnosed with it during their lifetime, according to the American Heart Association.

"It affects a lot of people. Of those who have heart failure, about half will die within five years of being diagnosed," Young said, noting that transplants are rare and most with the condition manage it through medication. "But it is associated with a reduced quality of life."

One expert praised the research.

"This is a nice paper showing the importance of physical activity to reduce the risk of heart failure," said Dr. Chip Lavie, medical director of cardiac rehabilitation and prevention at the John Ochsner Heart and Vascular Institute, in New Orleans.

"Numerous studies suggest that low cardiorespiratory fitness is perhaps the strongest cardiovascular risk factor. Probably the strongest contributor to cardiorespiratory fitness is regular physical activity and exercise training, but there also is a genetic component," said Lavie. "If two people do exactly the same amount of physical activity and exercise, one may still do considerably better in a race or a fitness test due to better natural ability and genetics."

Lavie said the study could be further refined by having the men use a pedometer to track their physical activity. A treadmill test could be added as well, to test heart and lung fitness, he noted.

He suspects the results would be the same in women.

Young said that even when she and her colleagues looked at people who developed heart disease or high blood pressure during the study, they found that being more active was still good. "It was more likely to protect against heart failure for those who had those conditions."

For those with heart issues who want to increase their exercise, it's not too late, she said, although, "obviously they have to get a clearance from their physicians before changing their physical activity."

The take-home message is simple, Young said: Sit less, move more.

"It doesn't even require joining a gym," she said. "Walking is the best exercise for the majority of people. Brisk walking. Thirty minutes a day is wonderful."