One of the new frontiers in the battle against heart disease focuses on children and the development of personality traits that may make them susceptible to heart attacks, high blood pressure and stroke. In particular, researchers are hunting for the early roots of type A behavior -- the aggressive personality traits linked to an increased risk of cardiovascular disease.

Studies suggest that type A behavior takes hold very early in life. In some cases, children just 3 to 6 years old already exhibit these potentially harmful personality traits.

The theory is that type A personality traits "emerge early in life, are stable over time and have a heritable component," says Karen Matthews, a University of Pittsburgh psychologist who specializes in the study of type A behavior.

Type A behavior is "the chronic struggle to achieve the most in the shortest period of time," Matthews explains. "It is characterized by extremes of competitiveness, impatience and easily aroused hostility." There is often, she adds, "an element of annoyance when anything impedes the progress of the type A person."

Researchers found that type A children, like type A adults, "show overt signs of irritation when frustrated." They are aggressive in play, competitive and perform at a very rapid rate on a series of tasks, whether they have a deadline or not. These youngsters also "suppressed fatigue, even when they were doing a fatiguing task."

Being type A, however, is not always bad. "Since more than 50 percent of the population can be classified as type A, this personality shouldn't be regarded as a psychopathology," says medical psychologist David Krantz of the Uniformed Services University of Health Sciences in Bethesda. "It's still a complicated question." Type A people are likely to be the superachievers -- the people who excel in school and sports. Their hard-driving type A traits have helped them be successful.

But since the landmark work by Drs. Ray Rosenman and Meyer Friedman first coined the term type A behavior, researchers and clinicians have come to recognize that these common personality traits can be predictors of who will develop hardening of the arteries (atherosclerosis) and subsequent heart disease.

Heart disease "typically strikes men in their mid-forties and women in their menopausal years," says Matthews. But research has shown that the foundation of heart disease actually starts much earlier in life, probably in childhood. Prevention efforts focus on better nutrition, exercise, weight control and now on minimizing the ill effects of type A behavior.

The discovery that type A behavior begins in children and adolescents comes from several types of observations.

The personality traits of type A children closely resemble the traits of type A adults. (One European study found evidence of this behavior in 3-year-old boys.)

Physically, these behaviors also seem to change the way the body's sympathetic nervous system responds to the normal stresses of everyday life in both children and adults. In general, people with type A behavior seem to show higher heart rates and blood pressure than those without it. These people may also produce higher blood levels of catecholamines and cortisol -- substances linked to an increased risk of heart disease.

Studies show some striking differences between youngsters with type A traits and their more relaxed counterparts, known as type B children.

Matthews and her colleague Dick Jennings set up special video games in a classroom -- where they felt the children would feel more at home -- to test children's responses to stress.

The youngsters competed against themselves in the first part of the study, but were told to "keep the ball in play as long as possible without any misses." During a second phase, the children played against a computer.

As a measure of impatience -- an important component of type A behavior -- the researches counted how many times a child moved the flippers on the game while waiting for another ball.

The type A children were much more impatient, says Matthews, and "in general, the type A kids had a higher heart rate and blood pressure than the type B children," a finding that was maintained throughout the game. Many factors, including parents, community, ethnic and religious values, probably play a role in the development of type A behavior.

Parents are role models for expressing anger, showing aggression toward others, dealing with frustration and setting goals and standards for work and play. "Parents shape children's willingness to delay gratification," Matthews says, and they teach youngsters about perceiving and responding to "threats to their sense of control and well-being." They also help set standards for children's relationships with others and for achievements.

To understand the role parents play in shaping type A behavior in their children, Matthews and her colleague David Glass studied how mothers instructed their children in a specific task.

The youngsters were blindfolded and had one arm tied behind their backs. Then the children were told to do special tasks with blocks and figures. Mothers were allowed to offer as much encouragement, help and guidance as they wanted (or none at all), but could not do the task for their younsters.

Matthews reports that "type A children experienced a very different kind of behavior in this situation with their mothers than type B children did." Type A children were told to improve their performance more frequently. "They would hear things like, 'That's fine, five blocks are good, but let's try for six,' " Matthews says. Type A children were also encouraged to "go faster," and were egged on to be perfectionists.

Overall, mothers of type A children drove their children harder, encouraging them to improve their performance, but offered little positive feedback as a reward. A companion study teamed these same children with mothers other than their own, and found that encouragement to perform was reinforced by many more positive remarks.

While type A children may not be rewarded very much by their own mothers, they are rewarded by strangers -- teachers, coaches and later in life, by bosses. They learn that society values people "who can think, play and work harder than others," Matthews says. "This makes us think that once type A gets going, it seems to be reinforced by the environment at the same time that these children experience higher and higher standards being set for them . . . Once type A behavior is exhibited, it is encouraged to be exhibited again."

As type A research continues, investigators are beginning to tease out several subcomponents of type A behavior that may be the real culprits in promoting cardiovascular diseases. Anger and hostility seem to play an important role. Anxiety and paranoia may contribute, too. There also appears to be a subgroup of type A people known as "hot reactors" -- individuals who show extreme changes in heart rate, blood pressure and hormone levels when confronted with stress.

If these subgroups of type A personality continue to be linked to the development of heart disease, then researchers may have a marker that could be important in early detection -- perhaps even in childhood -- of people likely to be victims of heart attack and stroke. The idea would be to screen the general population and then help these high-risk people change their behavior before heart disease progresses. Whether that can be accomplished among children, says Krantz, "is the $64,000 question."