Echocardiographic abnormalities have been identified in 14% to 62% of the patients with PM/DM. Transthoracic echocardiography can identify chamber hypertrophy and/or enlargement, diastolic dysfunction, hypokinesis, valvular abnormalities, pericardial involvement, and elevation of pulmonary pressures, all of which can be seen with underlying autoimmune myopathies. Yet, the changes associated with inflammation cannot be reliably detected. Hence, gadolinium-diethylenetriamine pentaacetic acid-enhanced cardiac MRI has been increasingly used to identify cardiac involvement in these patients. MRI can help to noninvasively identify the location and extent of myocardial inflammation and can serve as a roadmap if a biopsy is deemed necessary. When compared with endomyocardial biopsy, the diagnostic sensitivity, specificity, and accuracy of cardiac MRI has been found to be 76%, 54%, and 68%, respectively, in all patients with suspected acute or chronic myocarditis. The best diagnostic performance has been observed in patients with suspected acute myocarditis (sensitivity, 81%; specificity, 71%; and accuracy, 79%). Importantly, the kinetics of the characteristic contrast enhancement on MRI markedly improves after the appropriate treatment, suggesting this could be a useful biomarker for diagnosis and response to therapy.