A 14-year-old boy presented with the symptoms and clinical signs of myocarditis. Ventricular arrhythmias were the main manifestation. Dilated left ventricle with slightly impaired contractility and spongy appearance of the myocardium were also noted. Laboratory signs of an acute infectious disease were absent, but a significant rise in the complement fixation titer for Coxiella burnetii was observed. Treatment with oral tetracycline for 6 months resulted in improvement of ventricular arrhythmias and normalization of left ventricular dimensions and structure over the following months. Cardiac involvement in Q fever is rare, and with it endocarditis is usually seen as a chronic form of the disease. Myocarditis associated with Q fever has been reported only in some rare cases but not in children. The case reported here illustrates that the diagnosis of Q fever should also be considered in a case of myocardial involvement in an infectious disease of unknown etiology.