Children who are overweight are three to five times more likely to suffer a heart attack or stroke before they reach the age of 65, experts warn.
Experts are hoping to encourage children to exercise
The World Heart Federation says the unhealthy lifestyles increasingly adopted by children are behind the increased risk.
They warn obesity, poor diets, smoking and physical inactivity, are now being seen at an alarmingly early age.
They have issued the warning to mark World Heart Day next Sunday.
'Smoking before 10'
Children and adolescents will be encouraged to take part in fitness sessions to mark the day.
Experts also warn that more children are risking their future heart health through smoking.
The WHF says that across the world, 25% of all students smoke, having lit their first cigarette before the age of ten.
It adds almost half of all the children worldwide being subjected to passive smoke as they live in the home of a smoker.
Children who are regularly exposed to second-hand smoke involuntarily suffer from many of the diseases of active smokers and have a 25% increased risk of developing both lung cancer and heart disease and an 80% increased risk of suffering a stroke.
Sania Nishtar, chair of the Foundations Advisory Board for the World Heart Federation, said: "We must protect children from an environment that leads to heart disease by teaching life-long healthy eating habits and limiting exposure to unhealthy food.
"Children and adolescents who have balanced, nutritious diets, exercise regularly and resist the pressure to start smoking, should grow into fit, healthy adults.
"Increasing levels of physical activity is an immediate priority as two thirds of children worldwide are insufficiently active for their health."
Professor Poole-Wilson, President of the World Heart Federation, added: "We hold World Heart Day to encourage the world's population to lead a healthier lifestyle by taking more physical exercise and reducing the risk of heart disease through smoke-free living, healthy nutrition and weight control, amongst other measures.
"We also call on governments to get involved and adopt and implement policies which will work to reduce the risk factors for heart disease and stroke."