A case of a 44-year-old female patient is described, examined for several weeks with shortness of breath and the symptoms of heart decompensation after repeated untreated respiratory infections. Echocardiographically determined diffuse hypokinesis of dilated left ventricle with ejection fraction of 20%. Coronarographic examination without any significant finding at the coronary bed. MRI of the myocardium supported the suspicion of myocarditis, followed by the endomyocardial biopsy with electron microscopic evidence of borrelia fragments. After the causal and symptomatic treatment, the patient experienced significant clinical improvement and full normalisation of the finding.