WASHINGTON - Be happy - it seems to be good for your heart.

Scientists have long known that Type A personalities and people who are chronically angry, anxious, or depressed have a higher risk of heart attacks.

Now a Harvard review of the flip side of that psychology concludes that being upbeat and optimistic just might help protect against heart disease.

Rather than focusing only on how to lessen heart risks, "it might also be useful to focus on how we might bolster the positive side of things," said lead researcher Julia Boehm of the Harvard School of Public Health.

Boehm reviewed dozens of studies examining a positive outlook - as determined by various psychological measurements - on heart health. Optimism, in particular, seems key, as a number of studies found the most optimistic people had half the risk of a first heart attack when compared with the least optimistic, Boehm said.

Why? Previous work shows that stress associated with negative psychological traits can lead to damage of arteries and the heart itself.

Boehm found that people with a better sense of well-being tended to have healthier blood pressure, cholesterol, and weight, and are more likely to exercise, eat healthier, get enough sleep, and avoid smoking.

But she cautioned that it would take more research to tease apart whether a positive outlook makes people feel more like taking heart-healthy steps - or whether living healthier helps you feel more positive.

The review, funded by the Robert Wood Johnson Foundation, was published Tuesday by the Psychological Bulletin.

More research is needed, but the link between psychological and physical well-being makes sense, said Elizabeth Jackson of the University of Michigan and the American College of Cardiology, who was not involved with the review. Among her own heart patients, she has noticed that those who feel they have some control over their lives and are invested in their care have better outcomes.

What if you're by nature a pessimist? "That's a hard question," she said. "There's no magic happy pill."

Some research has found that asking people to smile helps put them in a better mood, Boehm noted, although long-term effects are not clear.

"Sometimes it's hard, particularly in tough economic times," Jackson said, "but taking a moment to just relax and enjoy a sunny day might be good heart health."