Myocarditis is an infectious-inflammatory disease with viral infections being one of the most common infectious cause. When it is superimposed to an individual genetic background, myocarditis may progress into a chronic heart muscle disorder, most often dilated cardiomyopathy (DCM), with a natural history similar to classic forms of genetic or idiopathic dilated cardiomyopathies. We present the case of a 30-year-old patient, with a persistent infectious episode in the last 8 weeks, pain and swelling in the large joints. At admission the patient had fever, tachycardia and a grade 2/6 systolic mitral murmur. Laboratory findings revealed inflammatory syndrome, hepatocytolysis syndrome and microalbuminuria. The electrocardiogram (ECG) showed possible right atrial tachycardia. The echocardiography revealed a globally enlarged heart with reduced ejection fraction and diffuse hypokinesia. When discussing the etiology of the DCM, the following were taken into consideration: a tachycardiomyopathy, ischemic etiology, genetic component, autoimmune etiology (elevated anti-Ro titer), and myocarditis. The diagnosis of myocarditis was confirmed by the cardiac magnetic resonance imaging which showed diffuse fibrosis of the interstitial space and an important increase of the extracellular volume. This case is distinguished by a particular immunological panel requiring dynamic monitoring in order to diagnose a possible associated autoimmune pathology.