Severely obese children are putting their heart at danger even while they are still in primary school, according to a Dutch study.
Heart disease is normally associated with middle age, but the early warning signs were detected in children between the ages of two and 12.
Two-thirds of the 307 children studied had a least one early symptom such as high blood pressure.
The findings were presented in Archives of Disease in Childhood.
Obesity is a growing problem around the world with more people becoming obese and at a younger age.
Two-year-olds with a Body Mass Index, a measure of obesity, greater than 20.5 are classed as severely obese. By the age of 18, a BMI of 35 is a sign of severe obesity.
Researchers at the VU University Medical Centre in Amsterdam collected data from the Dutch Paediatric Surveillance Unit between 2005 and 2007.
They looked at warning signs of heart disease in the severely obese children.
"Remarkably, 62% of severely obese children under 12 years of age already had one or more cardiovascular risk factors," the study concluded.
More than half had high blood pressure, and there were also cases of low "good cholesterol" and high blood sugar, which can result in Type 2 diabetes.
The researchers said this "may lead to cardiovascular disease in young adulthood".
Doireann Maddock, a senior cardiac nurse with the British Heart Foundation, said: "Although it was a small study, the findings leave a bad taste in the mouth.
"It's a huge concern so many obese children were identified as already having at least one risk factor for heart disease, including high blood pressure, high blood glucose and problems with cholesterol levels.
"However, this is a problem that can be addressed by stopping young people becoming overweight and obese in the first place.
"Highlighting the importance of healthy eating and physical activity from an early age will help protect the heart health of future generations."