Introduction: Childhood obesity is an important risk factor for the early cardiovascular disease. Studies show conflicting results on whether it is the diet or physical inactivity that play the most important role in treating childhood obesity and possible health consequences. Objectives: The aim of the study was to measure the cardiac function before and after three months intervention including only diet, continuous moderate exercise (CME) and high intensity aerobic interval training (AIT) in obese children/adolescents; to compare the cardiac function among exercise (CME+AIT) combined diet intervention with diet intervention only. Method: A randomized controlled trial study was performed. In total 29 obese (ISO-BMI ≥30 kg/m 2 ) children (16 girls, 13 boys) with mean age 11.3 ± 2.4 years and ISO-BMI 32.9 ± 3.3 kg/m 2 were randomized to either of three months intervention groups: Diet (32.8 ± 3.1 kg/m 2 ), CME (34.8 ± 4.3 kg/m 2 ) and AIT (31.2 .± 2.2 kg/m 2 ) respectively. The CME performed training at 70% of maximal heart rate (HR max ) for 47 minutes and the AIT performed 4×4 minutes training at 85-95% of HR max with 3 minutes active interval (60% HR max) in between. Both intervention groups performed the training session twice in the lab and once at home in each week for consecutive 12 weeks. Diet intervention together with AIT and CME were counseled together with their caregiver for healthy food choices for every second weeks for consecutive three months of intervention period. Anthropometric measurement with body composition, maximal oxygen uptake and resting echocardiography were done before and after intervention program. Mean ± standard deviation was calculated. Paired t-test and one way ANOVA test was used to compare the mean differences within and between the groups from baseline to three months test. The statistical significance of p