Cardiac magnetic resonance has become a reliable imaging modality providing structural and functional data, and fundamental information about tissue composition. Cardiac magnetic resonance imaging with late gadolinium enhancement, T1-mapping, T2-mapping, T2*-imaging, and extracellular volume, has proved to be a valuable tool in investigating the etiology of heart failure. Such analysis is helpful for the diagnostic evaluation of both ischemic and non-ischemic cardiomyopathies. As primary heart muscle diseases, the ability to characterize the myocardial substrate is essential. Determining the heart failure etiology is fundamental and has implications regarding the prognosis prediction and best treatment. Investigation in cardiac magnetic resonance in heart failure patients has grown in the past decade, and the true value of this imaging modality to detect early disease likely remains underestimated. This review describes the importance of cardiac magnetic resonance for the diagnosis and prognosis of non-ischemic cardiomyopathies, particularly hypertrophic, infiltrative, and arrhythmogenic cardiomyopathies.