The present study was primarily designed to validate the modified Haller index (MHI), the ratio of chest transverse diameter over the distance between sternum and spine, measured by a ruler and transthoracic echocardiography (TTE), respectively, in a cohort of subjects with obesity, but otherwise healthy, by comparing the results to the conventional Haller index (HI) measured on chest X-ray (CXR). 100 consecutive subjects with body mass index (BMI) ≥ 30 kg/m and 60 matched controls with BMI < 30 kg/m, who underwent a two-plane CXR for any clinical indication, were prospectively examined over a 6-month period. All participants underwent MHI assessment, TTE and speckle-tracking analysis of left ventricular (LV) global longitudinal strain (GLS). Bland-Altman analysis was used to compare the radiological and nonradiological techniques. Second, independent predictors of subclinical myocardial dysfunction, defined as LV-GLS less negative than - 20%, were evaluated. Bland-Altman analysis revealed a bias of - 4.91 cm for latero-lateral thoracic diameter, of - 0.74 cm for antero-posterior (A-P) thoracic diameter and of - 0.22 for HI assessment, suggesting a systematic overestimation of the nonradiological methodology in comparison to that radiological. Despite normal LV systolic function on TTE, LV-GLS resulted impaired in 76% of subjects with obesity. Waist circumference (OR 1.13, 95%CI 1.04-1.22) and nonradiological A-P thoracic diameter (OR 0.51, 95%CI 0.28-0.93) were the main independent predictors of subclinical myocardial dysfunction in subjects with obesity. The impairment in LV myocardial strain detected in subjects with obesity appears to be primarily related to extrinsic abdominal and thoracic compressive phenomena, rather than intrinsic myocardial dysfunction.