Arrhythmogenic cardiomyopathy (ACM) is a broad term that covers all arrhythmogenic myocardial disorders (including Arrhythmogenic right ventricular cardiomyopathy) in which arrhythmia is the main manifestation and is not related to ischemia, hypertension, or valvular heart diseases. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is best characterized by RV-origin ventricular arrhythmia and myocardial abnormality (fibrofatty replacement). However, biventricular involvement is not uncommon, and a small portion of ARVC patients have predominant LV involvement. So the term ACM was proposed to better define the full range of phenotypic variants. In this chapter, we discuss the terminology and latest diagnostic approach for ARVC, present the role of echocardiography in the diagnosis, and assess challenging cases of ARVC patients. Isolated left ventricular noncompaction (LVNC) is characterized by excessive LV trabeculation, most prominent in the apex, mid-lateral and inferior segments of LV, demonstrating an increased noncompaction-to-compaction ratio. Complications associated with non-compaction cardiomyopathy include heart failure, thromboembolic events, ventricular tachycardia, and sudden death. However, recent studies favor considering LVNC as a variant phenotype rather than an inherent cardiomyopathy.