June 30, 2004 -- The hearts of very obese kids often undergo a dangerous change, a new study shows.

The change is a thickening of the muscles of the heart. This puts a person at high risk of a heart attack, notes Thomas R. Kimball, MD, of Cincinnati Children's Hospital Medical Center.

Kimball's team used an ultrasound device to look at the hearts of 340 patients at their hospital. The kids were there either for medical problems, or for an evaluation for a gastric bypass procedure. Their average age was 12 years old. Their body mass index or BMI (a measure of weight relative to height, and an indicator of body fat) ranged from normal to extremely obese.

The finding: The higher the BMI, the more likely it was that the young person had alarming thickening of muscles of the heart.

"Extreme morbidly obese young patients are a particularly high cardiac risk group, even more than their overweight and obese counterparts," Kimball says in a news release.

Kimball's team reported the findings at this week's annual meeting of the American Society of Echocardiography in San Diego.