Insulin resistance (IR) and inflammation are associated with an increased risk of cardiovascular disease and may contribute to obesity cardiomyopathy. The earliest sign of obesity cardiomyopathy is impaired left ventricular (LV) diastolic function, which may be evident in obese children and adolescents. However, the precise metabolic basis of the impaired LV diastolic function remains unknown. The aims of this study were to evaluate cardiac structure and LV diastolic function by tissue Doppler imaging in overweight and obese (OW) youth and to assess the relative individual contributions of adiposity, IR, and inflammation to alterations in cardiac structure and function. We studied 35 OW (body mass index standard deviation score 2.0 ± 0.8; non-IR n= 19, IR n= 16) and 34 non-OW youth (body mass index standard deviation score 0.1 ± 0.7). LV diastolic function was reduced in OW youth compared with non-OW controls, as indicated by lower peak myocardial relaxation velocities (p