But what is type D? First defined in the 1990s, type D denotes a generally anxious, irritable and ill-at-ease personality type. These men and women lack self-assurance, hesitate to share their feelings with others and fear disapproval—rather like Winnie-the-Pooh's gloomy friend Eeyore.

Type D adults who have already been diagnosed with a heart problem are significantly more likely to face future heart difficulties than those with sunnier dispositions.

An analysis of studies involving more than 6,000 heart patients noted a threefold increase in long-term risk of additional cardiac issues—including narrowing of the arteries, heart attack and heart failure—among those with type D "distressed" personalities. They also are more likely to need angioplasty or bypass surgery and to die prematurely. Senior author Johan Denollet, a medical psychologist at Tilburg University in the Netherlands, points out that those with a type D personality tend to have heart problems independent of traditional medical risk factors such as high blood pressure and high cholesterol.

The reasons for the higher risk are not clear, but type Ds seem to respond to stress differently. They show artery-damaging inflammation as well as increased levels of the stress hormone cortisol, which is linked to high blood pressure. In addition, they are less likely to have medical check-ups, pay attention to their doctors' recommendations or take prescribed medications.

A type D personality profile can be determined using a brief test of 14 statements such as: "I find it hard to start a conversation" and "I often find myself worrying about something."

Type D is not depression. "It's a combination of normal personality traits that make it hard to change your life," says Denollet, "and it's quite common." Screening heart patients for type D could provide a chance for doctors to help them learn new strategies to reduce their level of distress.

"We're beginning to understand that emotional state is an important component of overall health, and we need to be aware that personality does matter," says Clyde Yancy, M.D., medical director of the Baylor Heart and Vascular Institute in Dallas and past president of the American Heart Association. "But we must never lose sight of the fact that traditional risk factors such as obesity, high blood pressure, physical inactivity and poor diet trump everything else when it comes to heart disease."

The type D study was published Sept. 14 in Circulation: Cardiovascular Quality and Outcomes.

Nissa Simon, a health writer, lives in New Haven, Conn.