Diabetes is associated with reduced aerobic capacity and impaired left ventricular function. Large cohort studies show that people with diabetes are also more likely to develop ischaemic heart disease and heart failure. It is assumed that morphological and autonomic changes resulting from chronic hyperglycaemia and/or hyperinsulinemia contribute to diabetic cardiac dysfunction. It is less clear whether adolescents, whose diabetes duration is relatively shorter, also have reduced cardiac reserve and impaired left ventricular function. This presentation will describe the left ventricular response to acute exercise in adolescents with diabetes and how exercise training affects the adolescent diabetic heart.