Diagnosing left ventricular noncompaction (LVNC) cardiomyopathy is a challenge for the medical community because the condition shares morphologic features of hypertrophic and dilated cardiomyopathies. The uncertainty surrounding the diagnosis of LVNC is related to the lack of a “perfect diagnostic tool,” such as a reproducible genetic marker. The diagnosis requires expertise in the broad spectrum of overlapping cardiomyopathies. The demarcation between LVNC and normal phenotypic variations is often indistinct. Echocardiography, used in routine clinical practice to identify the typical morphologic features of LVNC, can be overly sensitive and lack specificity with the presently defined measurements and ratios used to diagnose LVNC. The available diagnostic criteria show a propensity toward overdiagnosing LVNC. The complex clinical sequelae of atrial and ventricular arrhythmias, heart failure, thromboembolic events and sudden death associated with LVNC make a valid and reproducible diagnosis critical. The trend to using a morphologic/pathophysiologic, instead of a solely morphologic, approach holds promise in the quest for an accurate, reliable diagnosis of LVNC. We must understand the distinction between morphological findings and morphological findings with pathophysiology. Our future understanding of LVNC depends on an integration of cardiac morphology, physiology, pathophysiology and evolving genetics.  (Circ J 2012; 76: 1556–1562)