Those who were the most optimistic had about a 50% reduced risk of having a heart attack or stroke compared to those who were less satisfied with their lives.
Scientists don't know all of the reasons why optimists have healthier hearts but they suggest that part of it has to do with better handling of stress.
People with a positive outlook were also more likely to live a healthier lifestyle, by exercising, eating a healthy diet and getting the proper amount of sleep.
Scientists know that depression, and using negative emotions such as hostility, anger and anxiety to deal with issues or suffering can be harmful to the heart.
The researchers hope their findings can be used as an intervention strategy to give doctors another tool in the battle against heart disease.