Even if you're grumpy by nature, just try to be cheerful.
Researchers at Columbia University rated the happiness levels of more than 1,700 adults in Canada with no heart problems in 1995.
After a decade, they examined the 145 people who developed a heart problem and found happier people were less likely to have had one.
The study was published online Thursday in the European Heart Journal.
"If you aren't naturally a happy person, just try acting like one," said Dr. Karina Davidson of Columbia University Medical Center, the paper's lead author. "It could help your heart."
Davidson and colleagues used a five-point scale to measure people's happiness. They then statistically adjusted to account for things like age, gender, and smoking.
For every point on the happiness scale, people were 22 percent less likely to have a heart problem. The study was paid for by the U.S. National Institutes of Health and others.
Davidson said happy people were more likely to have a healthier lifestyle.
It could also be there is an unknown genetic trait that predisposes people to be happy and have less heart disease.
Other experts said happiness itself could result in a healthier heart compared to other emotions such as stress or depression.
Stress often releases hormones that can damage heart muscle. Stress can also cause blood vessels to open too wide, allowing plaque buildups to break off and clog the arteries, according to Joep Perk, a professor of health sciences at Sweden's Kalmar University and spokesman for the European Society of Cardiology. Perk was not linked to the study.
"I often tell my patients not to get too depressed because it's bad for your heart," Perk said. "You need time to recharge your batteries or else your heart won't be able to take it."
Depression has long been noted as a risk factor for heart problems. Davidson said it was premature to draft guidelines recommending patients boost their happiness levels just to protect their hearts, even if it might help, until broader studies now under way are completed. But she does recommend trying to be happy for other reasons, like better mental health.
"Anything that patients can do to increase the amount of (happiness) in their lives will be helpful," she said, adding there was a slight proviso. "No smoking, eating unhealthy food, not exercising or anything potentially damaging," she said. "That's the only trick."