BACKGROUND: Echocardiographic characteristics typical of isolated left ventricular noncompaction (IVNC) have been well defined. The aim of this study was to validate diagnostic criteria of IVNC in valvular or hypertensive heart disease (HHD) or dilated cardiomyopathy. METHODS: We conducted a retrospective analysis of records and blind review of videotapes of all 19 patients with IVNC seen within 7 years in comparison with randomly selected patients from the same study period with dilated cardiomyopathy (31 patients), HHD (22 patients), and chronic severe valvular heart disease: mitral regurgitation (22 patients); aortic regurgitation (20); and aortic stenosis with bicuspid (22) or tricuspid (22) valves. RESULTS: Clinical characteristics and electrocardiographic findings did not differ between IVNC and other diseases. In IVNC, all patients had noncompacted (NC) segments with a 2-layered structure and wall thickening, and in most patients perfused recesses (95%) or hypokinetic segments (89%) were present. Both hypertrabeculation or presence of a meshwork were specific for IVNC, but the sensitivity for IVNC was only 11% for hypertrabeculation, respectively, 68% for meshwork. In dilated cardiomyopathy, perfused recesses (48%) and a 2-layered structure (26%) were seen but without wall thickening of these segments; all NC criteria including wall thickening were fulfilled in one patient (3%) only. In valvular heart disease or HHD, perfused recesses and a 2-layered myocardium were rare: two patients (5%) with aortic stenosis and one patient with HHD (5%) had NC. Although in IVNC wall thickening was confined to the 2-layered myocardial segments, it was diffuse in other diseases. CONCLUSIONS: Although some NC criteria are occasionally found in other heart disease, the combination of all criteria is very specific. All criteria of NC are rarely met in other disease than IVNC (< or = 5%).