Keeping a positive attitude is good for your heart, suggests new research.

A study of patients with heart disease found that those with pessimistic beliefs about their recovery were twice as likely to die within a 10-year timeframe as those who felt more optimistic.

The findings aren't altogether new. Previous studies have linked depression as well as anxiety to higher death rates from heart disease. But there has been less research on the mechanisms behind the link.

Two studies presented this week at the annual meeting of the American Psychosomatic Society, a group dedicated to the research of the interaction between the mind and body, provide some clues.

The first study from researchers at Duke University Medical Center conducted psychological assessments on 2,825 patients who had been diagnosed with heart disease. The patients were asked about their expectations about their ability to recover and regain a normal life.

During six to 10 years of follow-up, 978 of the patients died, 66 per cent of them from heart disease.

The researchers found that patient expectations about their disease outcome were highly related to survival. Those who had the most pessimistic views died at twice the rate of those who were most optimistic.

After controlling for factors that could influence survival, such as disease severity, the death rate among the most pessimistic patients was still 30 per cent higher than the most optimistic.

The study authors say patients with positive expectations may be more likely to make lifestyle changes to improve their health. They are also most likely to take their medications and follow the recommendations of their doctors.

The second study looked at one of the theories about how depression can affect the heart: that depression promotes stiffening of the heart tissue, which worsens heart failure, since the heart becomes inflexible and can't pump blood as well.

Researchers from University of Maryland School of Medicine looked at 880 adults and measured proteins in the blood that indicate stiffening of heart tissue. They also checked for C-reactive protein, another protein in the blood that is linked to inflammation.

They found that the depressed adults had higher levels of this C-reactive protein and more inflammation.

They believe that the inflammation plays a key role in explaining why depressed adults have stiffer heart tissue.