Cardiomyopathies are the leading cause of sudden cardiac death in young athletes. The electrocardiogram (ECG) is utilized as a first-line screening and diagnostic tool for detecting conditions associated with sudden death. Fundamental to the appropriate evaluation of athletes undergoing ECG is an understanding of what ECG findings are abnormal and may suggest the presence of a pathologic cardiac disorder. Multiple findings such as T-wave inversion, ST-segment depression, and pathologic Q waves are present in patients with cardiomyopathy. This article reviews the ECG findings in the four most common cardiomyopathies afflicting young athletes - hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, left ventricular noncompaction, and idiopathic dilated cardiomyopathy. ECG changes resulting from physiologic cardiac adaptation to regular exercise (athlete's heart) are presented also. This article provides a framework for distinguishing normal from abnormal ECG findings and outlines appropriate steps for further evaluation of ECG abnormalities in athletes suspected of having a cardiomyopathy.