To assess cardiac anatomy and myocardial systolic function in children with Prader-Willi syndrome (PWS).Physical examination, electrocardiographic (ECG) recordings and transthoracic echocardiograms including two-dimensional speckle tracking echocardiography (2DSTE) were performed and evaluated in the Radboud University Hospital Nijmegen, the Netherlands. In total, 19 children diagnosed with PWS and 38 age-matched control subjects underwent cardiac evaluation.Abnormal ECG findings were detected in nine PWS patients. Echocardiography revealed mild structural cardiac abnormalities in two patients. Conventional echocardiographic findings did not indicate systolic left ventricular dysfunction, in contrast to 2DSTE examination. Global peak systolic strain (rate) measurements, in all three directions of contraction, were significantly lower in children with PWS (p < 0.001) compared with healthy age-matched children. In two-thirds of the patients, 2DSTE revealed abnormal systolic deformation (peak systolic strain as well as strain rate). T2P values in PWS patients were similar to control subject. Systolic myocardial function appears more affected in case of maternal uniparental disomy.Cardiac evaluation, including 2DSTE, detects frequent alterations in myocardial systolic function in children diagnosed with PWS, whose conventional echocardiographic findings did not indicate ventricular systolic dysfunction. Because cardiovascular morbidity and mortality is substantial in PWS, especially adults, we emphasize the need for cardiac assessment in PWS.