Background: Left ventricular noncompaction (LVNC), also termed spongy myocardium, is diagnosed by echocardiography or cardiac magnetic resonance imaging (CMR). The aim of this study was to assess the criteria for diagnosis of LVNC by echocardiography and CMR. Methods and Results: CMR images of 19 echocardiographically diagnosed LVNC patients were obtained (10 males, 3m to 12y of age). Left ventricular noncompaction was diagnosed by CMR in 12 cases. Patients with CMR-diagnosed LVNC were more often males (58% versus 53%), had an impaired LV contractility (66% by CMR versus 21% by echocardiography), showing myocardial fibrosis (25% by CMR versus 10% by echocardiography), showing abnormal mitral valve (42% by CMR versus 68% by echocardiography), showed aortic root dilatation (25% by CMR versus 31% by echocardiography), showed congenital heart anomalies (33% by CMR versus 36% by echocardiography). Conclusions: Echocardiographic definition for CMR yielded the diagnosis of LVNC in only 63%.When looking for LVNC by CMRI, LV size, function, and extension of LVNC,fibrosis have to be considered.