OBJECTIVES: It is known that obesity is related to heart failure. Asymptomatic left ventricular diastolic dysfunction (LVDD) is associated with the development of heart failure. The relationship between subclinical LVDD and overweight in children is not clear. The purpose of this study was to evaluate the effect of body mass index (BMI) and waist circumference on left ventricular mass index (LVMI) and LVDD in overweight children. STUDY DESIGN: A total of 153 children were enrolled in the study. Of these, 91 were normal weight (age-adjusted BMI: 15-85 percentile), and 62 were overweight (age-adjusted BMI: 85-95 percentile). After measuring two-dimensional and M-mode echocardiographic variables, left and right ventricle diastolic functions were assessed by conventional and tissue Doppler imaging. RESULTS: Compared to controls, overweight children had increased left atrium, aortic and left ventricular diameters, left ventricular wall thickness, LVM and LVMI, and septal mitral annulus e', septal e'/a', lateral e', lateral e'/a', lateral tricuspid annulus e', and e'/a' values. There were negative correlations between tissue Doppler diastolic parameters (septal mitral annulus e', lateral mitral annulus e', lateral tricuspid annulus e', septal mitral annulus e'/a', lateral mitral annulus e'/a', and lateral tricuspid annulus e'/a') and BMI, waist circumference, insulin, HOMA index, as well as systolic and diastolic blood pressure. Positive correlations were found between LVMI and BMI and between LVMI and waist circumference. BMI was found to be the predictor of decreased mitral anulus septal e', septal e'/a', lateral e', lateral e'/a'. CONCLUSION: Compared with normal-weight children, overweight children have decreased LV diastolic function. BMI is associated with a reduction in LV diastolic function in overweight children.